Operating procedures for crude benzene processing

Thread Content

Chapter 1: Technical Specifications for Benzene Refining Process Section 1: Basic Principles of Benzene Refining The raw materials processed in the benzene refining workshop are purchased crude benzene and light benzene. Its main components are benzene and its homologs; benzene, toluene, xylene, etc. account for 80%–95% of it. In addition, there are aliphatic hydrocarbons, naphthenic hydrocarbons, unsaturated compounds, as well as small amounts of sulfides, pyridine bases, and acids such as the low-boiling fraction of cleaning oils. All the main components of crude benzene are distilled off before 180°C. Since crude benzene and light benzene are relatively complex mixtures, they have limited uses on their own; however, the purified products obtained through processing are important chemical raw materials with high economic value. The purpose of crude benzene refining is to obtain as much pure benzene product as possible, while making the most of other components as well. (1) Basic principle of the sulfuric acid washing purification method: Crude benzene contains 5–12% of unsaturated compounds and other impurities, which are mainly found in the fractions distilled at temperatures above 14°C and below 79°C. In the process using two benzene towers, unsaturated compounds in the heavy benzene at temperatures above 140°C are removed from crude benzene, thereby yielding light benzene and heavy benzene as two separate products. The purpose of the initial distillation of light benzene is to remove unsaturated compounds and carbon disulfide below 79°C. The resulting mixed fraction also contains unsaturated compounds and sulfide impurities with boiling points close to those of aromatic products, which can be purified by chemical methods. 1. The commonly used method is purification by sulfuric acid washing, and its main chemical processes are as follows: (1) Polymerization reaction of unsaturated compounds. Unsaturated compounds readily undergo polymerization in the presence of sulfuric acid; low-boiling-point compounds tend to form highly viscous polymers that are insoluble in both the mixture and sulfuric acid. It causes entrainment losses of the compound. Therefore, primary distillation must first be carried out to remove low-boiling unsaturated compounds. High-boiling unsaturated compounds have a low degree of polymerization; generally, only soluble dimers and trimers are formed. (2) Addition reactions: Unsaturated compounds of sulfuric acid can also produce acid-lipids and neutral lipids; the former are soluble in sulfuric acid, while the latter are soluble in mixed solutions. Low-boiling unsaturated compounds react with sulfuric acid to form neutral fats; during benzene distillation, these neutral fats heat up and decompose, releasing acidic substances that can corrode equipment. Therefore, it is necessary to remove low-boiling substances as much as possible during the initial distillation stage. (3) Thiophene removal reaction: Under the catalysis of concentrated sulfuric acid, thiophene can copolymerize with high-boiling-point unsaturated compounds to form copolymers that are soluble in the mixture; this reaction proceeds rapidly and completely. Thiophene can also dissolve directly in sulfuric acid, but the dissolution rate is very slow. (4) Copolymerization of aromatic hydrocarbons with unsaturated compounds: Aromatic hydrocarbons undergo copolymerization with unsaturated compounds in the presence of concentrated acid to produce copolymers that are soluble in the mixture. (5) Sulfonation of aromatic hydrocarbons: Aromatic hydrocarbons can undergo sulfonation when in contact with concentrated sulfuric acid, resulting in the loss of these aromatic hydrocarbons. 2. Key factors affecting sulfuric acid washing: (1) Reaction temperature. The most suitable reaction temperature is 35–45°C; too low a temperature results in a slow reaction and failure to meet the purification requirements, while too high a temperature accelerates the sulfonation of aromatic hydrocarbons as well as the copolymerization of unsaturated compounds, thereby increasing the loss of aromatic hydrocarbons. (2) Sulfuric acid concentration: A too low concentration of sulfuric acid fails to meet the purification requirements, while a too high concentration accelerates the sulfonation reaction and increases the loss of benzene derivatives; therefore, a suitable sulfuric acid concentration of 93–95% is chosen. (3) Ratio of sulfuric acid to the mixture: While ensuring the required washing quality, the lower the ratio of acid to oil, the better. It not only reduces acid consumption but also enables the sulfonation of aromatic hydrocarbons. (4) Reaction time: The time required for the pickling and purification reaction depends on factors such as reaction temperature, sulfuric acid concentration, degree of acidification, and mixing intensity. The typical reaction time is around ten minutes; if the time is too short, the reaction efficiency is poor, which inevitably leads to increased acid consumption. If the time is too long, the sulfonation reaction intensifies and there is more loss of benzene derivatives. Therefore, water must be added to the reactor immediately to terminate the reaction of concentrated sulfuric acid. During the washing process, the pyridines and phenols in the mixture can be removed due to the action of sulfuric acid and alkalis. (II) Basic principles of distillation: The mixture purified with sulfuric acid remains a complex mixture. To obtain a pure benzene hydrocarbon product, it can be separated using distillation. The principle of distillation is based on the fact that different components in a liquid mixture have varying degrees of volatility; at the same temperature, these components have different vapor pressures. Obviously, at the same temperature, components with a higher volatility evaporate more easily from the liquid. Similarly, if part of the mixture is condensed, components with a higher volatility are more difficult to condense. For example, in terms of the volatility of aromatic hydrocarbons in the mixture: benzene > toluene > xylene. If the benzene content in the mixture is high, then when this vapor is condensed, the most abundant compound to condense from the vapor is xylene, followed by toluene; as a result, the benzene content in the vapor remains high. If this steam is cooled using a liquid with the same composition as the steam, then as it is heated, the component with high volatility, benzene, will vaporize. As the steam cools down, the component with lower volatility, xylene, will condense. As a result, the benzene content in the steam increases, while the xylene and toluene contents in the liquid increase. By partially vaporizing and partially condensing in this way, an almost pure component can be obtained. The distillation process is essentially a physical process in which mass transfer and heat transfer occur simultaneously. Each tray in each distillation column performs the function of mass and heat transfer, with some vaporization and some condensation occurring at those trays. When this steam meets the cooler liquid stream flowing from top to bottom, condensation of the less volatile components in the steam occurs on each tray, while the more volatile components in the liquid evaporate due to the heat released during condensation. In a distillation column operating under continuous distillation, each tray maintains a constant temperature, which is suitable for achieving an equilibrium composition of vapor and liquid. The rising vapor stream continuously enriches components with high volatility, while the descending liquid stream continuously enriches components with low volatility. To obtain a product of high purity, qualified product is used as reflux at the top of the tower to enhance the processes of partial vaporization and partial condensation. During the distillation process, mass transfer and heat transfer occur simultaneously; therefore, a distillation column that operates stably is subject to both material balance and heat balance considerations. If either of these balances is disrupted, it will inevitably affect the stable operation of the distillation column. Section 2: Process Flow of the Pure Benzene Workshop (1) Washing Process Flow: The mixture from the unwashed tank is fed into the raw material surge tank T701 by means of the raw material pump P101A. Concentrated sulfuric acid is unloaded from the truck into the underground tank designated for receiving concentrated acid, and then pumped by an underground acid pump into the concentrated acid storage tank T714 for storage. During production, the concentrated acid is transferred from the concentrated acid storage tank T714 into the tank designated for receiving concentrated acid, from where it is pumped by an acid transfer pump into the concentrated acid storage tank T704. Liquid caustic is unloaded from truck tankers into the submersed tank designed to receive caustic, and then pumped using a submersible pump into the liquid caustic storage tank (24) for storage. During production, concentrated alkali is transferred from the liquid alkali storage tank (24) into the alkali receiving tank below the liquid level, and then pumped into the alkali mixing tank using a submersible pump for alkali. The diluted alkali resulting from the mixing process is pumped into the high-level alkali tank (15) using a submersible pump for diluted alkali (23). The unprocessed mixture from the raw material sump (12) and the concentrated sulfuric acid from the concentrated sulfuric acid sump (15) are fed into the spherical mixer (13) by the washing pump (B2) in a certain ratio, thereby allowing further mixing of the acid and the mixture. After that, the mixture enters the reactor (16), where the reaction takes place for about 10 minutes. Subsequently, it passes through the water addition mixer (17) and then into the acid-oil separator (18), where the acid and oil are separated from each other. The oil overflows from the upper part of the acid-oil separator, and an alkaline solution is continuously added in a certain proportion from the dilute alkali sump (15) to neutralize the acid contained in the oil. After being mixed in the alkaline addition mixer (20), the mixture enters the acid-alkali separator (19), from where the washed mixture flows over from the upper part of the separator into the storage tank for the washed mixture. The waste acid discharged from the bottom of the acid oil separator is sent to the acid tar sedimentation tank (21), where it undergoes further separation from the acid tar. The waste acid is then pumped, via the regenerated acid pump (B3), from the bottom of the acid tar sedimentation tank to the regenerated acid storage tank for transport away. The acid tar separated from the acid oil separator is discharged into the steam stripping vessel from the feed tank. (If the separation effect is poor, it is discharged into the acid tar sedimentation tank); the acid tar separated from the acid tar sedimentation tank is also sent to the steam stripping furnace, where it is neutralized using benzene alkali from the alkali oil separator (if the amount of waste alkali available for neutralization is insufficient, waste alkali from the dilute alkali storage tank is used instead). Then it is blown with direct steam, and the regenerated benzene is discharged through a steam blowdown cooler. The regenerated benzene oil is separated from water and then sent to the distillation system. The wastewater discharged from the regenerated benzene oil water separator is sent to the sewer system, while the acid tar at the bottom of the distillation tank is discharged into an acid tar storage tank for further transportation. (II) Steam distillation process flow: 1. Two benzene towers: Heavy benzene is removed to obtain light benzene. In the crude benzene feed tank (1), the feed is pumped by the feed pump (B4) into the crude benzene feed heater (3). After heating, it enters the bottom of the diphenyl tower (2), where it is heated indirectly by steam along with a reboiler (3); a small amount of direct steam is also supplied to extract the low-boiling-point components present therein. The temperature of the two benzene towers is maintained at around 140–150°C. The heavy benzene, after being cooled to 45–50°C, enters the heavy benzene storage tank (7). The light benzene vapor coming from the top of the diphenyl tower is condensed and cooled in the condenser (4) to a temperature of 18–30°C, after which it enters the oil-water separation unit (5). After the water is separated, the light benzene flows into the light benzene storage tank (8), where it is used as feed for the fractional distillation tower. At the same time, it is pumped back to the top of the diphenyl tower via the reflux pump (10) to maintain the tower top temperature at 75–82°C. 2. The initial distillation tower is used to remove the initial distillate, yielding an unprocessed mixed fraction. The feed for the light benzene tank (8) is pumped by the primary distillation feed pump (B6) into the primary distillation tower (13). A reboiler (6) is attached to the bottom of the tower, and it uses indirect steam heating to raise the temperature to around 90–94°C. The vapor resulting from the primary distillation at the top of the tower is cooled by a condenser (6) to a temperature of 18–30°C before entering the oil-water separator (5). The distilled product is then sent to the primary distillation tank (9), where part of it is fed back into the tower using the primary reflux pump (B7) in order to maintain the temperature of the 30th tray between 65–75°C; the remaining portion is stored. The mixture used at the bottom of the initial distillation tower is sent, via a cooler (6), to the unprocessed mixture tank (11) as raw material for the washing system. 3. Benzene stripping tower: Removes high-boiling-point oils and residual polymers from the washed mixture. The washed mixed mixture enters the washed mixture tank (26), and is sent to the benzene-blowing raw material heater (27) by the benzene-blowing raw material pump (B8) to be heated to around 105–115°C before entering the benzene-blowing tower (28). A bottom heater is installed at the bottom of the tower, and direct steam is used for blowing. The benzene emitted from the top of the benzene-blowing tower passes through a neutralizer (4), where the alkaline solution from the alkali oil separator (19) is pumped in by the circulation pump (B9) to neutralize acidic substances such as sulfur dioxide released upon the thermal decomposition of neutral fats. The alkaline solution flowing out from the bottom of the neutralizer passes through the alkaline solution cooler (28), and after oil is separated in the alkaline oil separator, the alkaline solution is recycled. The oil separated by the alkaline oil separator is sent to a drainage tank in the basement for recovery. The benzene that has been neutralized by the neutralizer goes to the benzene condensation cooler (4), where it is cooled to 18–30°C. Afterwards, it enters the benzene oil-water separator (5); the pure benzene then flows into the pure benzene raw material tank (30). The residues resulting from the benzene extraction process are sent to the benzene residue tank (29), from where they are transported outside via a steam pump (B10). 4. Benzene purification tower: Continuous extraction of pure benzene. The benzene to be blown out is continuously fed from the pure benzene feed tank (30) via the pure benzene feed pump (B11) into the pure benzene tower (31). A reboiler (3) is located outside the bottom of the tower and uses indirect steam heating to raise the temperature to 125–135°C. The pure benzene vapor emerging from the top of the tower enters the pure benzene oil-water separator (5) through the pure benzene top condenser (4). Part of this vapor is sent back to the top of the tower as reflux liquid by means of the pure benzene reflux pump (B12) in order to maintain a temperature of 79–81°C; the other part flows directly into the pure benzene storage tank (32) to be exported as a product. The pure benzene residue at the bottom of the tower is cooled to 18–30°C in the pure benzene residue cooler (6) before being stored in the pure benzene residue tank (33) to serve as raw material for the toluene tower. 5. Toluene tower: Continuous extraction of toluene. The pure benzene residue from the feed tank (33) is continuously pumped into the toluene column (34) by the toluene feed pump (B13). The bottom of the column is heated to 145–155°C using indirect steam from a reboiler; the toluene vapor that emerges from the top of the column passes through a condenser (4) before reaching the toluene oil-water separator (5). Part of the separated toluene is used as reflux and is pumped back to the top of the column by the toluene reflux pump (B14) in order to maintain a temperature of 109–110°C at the column top. The other portion flows as product to the toluene storage tank (35). The toluene residue discharged from the bottom of the tower is sent to the toluene residue tank (36) as a feed for the xylene tower. 6. Xylenes tower: for extracting xylene. The toluene residue is continuously fed from its storage tank (36) via the xylene feed pump (B15) into the bottom of the xylene tower (37), where a reboiler (3) is attached; it is heated using indirect steam as well as direct steam. Keep the temperature at the bottom of the tower around 140–145°C. The xylene mixed vapor exiting the top of the tower returns to the xylene oil-water separator (5) via the condensation cooler (4); a portion of this vapor is pumped back to the top of the tower by the xylene reflux pump (B16) as reflux, thereby maintaining the temperature at the top of the tower at 140–145°C. A portion of the flow is returned to the xylene storage tank (38) for shipment as a product. The xylene bottom stream, which consists of xylene residue, is discharged to the xylene residue tank (39) and is transported as a by-product. Section 3 Process Control Parameters
(I) Washing System
1. Oil temperature before the washing pump: 25–35°C
2. Acid addition rate (based on the raw material): 5–8%
3. Concentration of waste acid: 40–45%
4. Reactor temperature: 40–45°C
5. Concentration of alkali added: 11–13%
6. Amount of dilute alkali added: sufficient to make the oil slightly alkaline
7. Maximum distillation temperature in the distillation vessel: ≥95°C
8. Acid tar discharged from the bottom of the distillation vessel: alkaline in nature
9. Temperature of acid and alkali: 50–70°C
10. Concentration of sulfuric acid: >93%
11. The raw material (before washing) must be free of water.
12. The pressure from the steam used for adding alkali must not cause an increase in pressure inside the tank.

(II) Distillation System
Biphenyl towers, initial distillation tower, benzene distillation tower, pure benzene tower, toluene tower, xylene tower
Number of feed trays per m³/n: 1.5–2.5, 1.5–2.5, 1.5–2.4, 1.5–2.4, 0.3–0.5, 0.3–0.5
Reflux ratio relative to the raw material: 2.5–3.5, 0.3–0.8, 1.0–1.5, 1.5–2.5, 0.8–1.5
Boiler temperature (°C): 91–96, 125–130, 155–156, around 160
Top temperature of the tower (°C): 75–82, <60, 95–105, 80±0.5, 110±0.5, 90–100
Temperature of the liquid leaving the evaporator (°C): 110–120, 105–115
Bottom temperature of the tower (°C): 140–150, 90–94, 124–128, 150–155, 130–145
Temperature at the 5th tray (°C): 88–89, 108–115, 136–141, around 130
Temperature at the 30th tray: 65–75, 8.2–8.3, around 113, 110–120
Bottom pressure of the tower (kg/cm²): <0.35, <0.4, <0.3, <0.4, <0.4, <0.35
Pressure of heating steam (kg/cm²): 1–1.5, 3–4, 5–7; indirect heating: 8, direct heating: 1
Liquid level at the bottom of the tower: 1/2–2/3, 1/2–2/3, 1/2–2/3, 1/2–2/3, 1/2–2/3, 1/2–2/3
Oil temperature at the exit of the condenser: 15–30, 15–30, 15–30, 15–30, 15–30, 15–30
Water temperature at the exit of the condenser: <45, <45, <45, <45, <45, <45
Oil temperature at the exit of the residue oil cooler (°C): 25–35, 20–30, 20–30, 20–30
Note: Parameters for the xylene tower refer to those when producing 10°C xylene using direct steam. Section 4: Analysis and Testing System
Sample Name, Quality Requirements, Analysis Items, Sampling Time and Location
Crude Benzene: Specific gravity 0.871–0.900; distillation yield before 180°C ≥ 93%; boiling point in distillation test; distillation yields at 100°C, 125°C, 150°C, and 160°C; specific gravity measurement. Analysis is conducted once upon leaving the tank and after each batch of material processed.
Light Benzene: Specific gravity d4^20 ≤ 0.88 (dry point ≥ 96%, ≥ 150°C); distillation test, boiling point; temperature measurements at 10%, 20%, …, 90% distillation yield; specific gravity and colorimetry measurements. Analysis is carried out once per shift.
Weak Alkali: Concentration 11–13%; d4^15 = 1.125–1.145; specific gravity measurement. Analysis is done once per shift.
Waste Acid: Concentration 40–45%; d4^20 = 1.30–1.35; specific gravity measurement. Analysis is done once per shift.
Unwashed Powder: Boiling point > 82°C; CS2 content < 0.05%. Boiling point measured in distillation test. Analysis is conducted every two hours.
Washed Powder: Colorimetry value ≤ 0.5; bromine value; colorimetry measurements. Analysis is done every two hours.
Benzene Distillate: Product specifications for release; colorimetry and distillation test measurements. Analysis is conducted every two hours.
Pure Benzene Residue: Boiling point ≥ 183°C; distillation test and boiling point measurements. Analysis is done twice per shift.
Toluene: Product specifications for release; colorimetry and distillation test measurements. Analysis is conducted every two hours when the tank is full. Toluene residue: Boiling point ≥ 138°C; distillation test and boiling point measurements. Analysis is done twice per shift.
Xylene: Product specifications for release; colorimetry and distillation test measurements. Analysis is conducted hourly when the tank is full. Xylene residue: Boiling point ≥ 155°C; distillation test measurements. Analysis is done once per shift.
Initial Distillate: Distillation yield before 80°C > 90%; distillation test and boiling point measurements before 80°C. Analysis is done once per shift.
Residue from Distillation Process: Oil content < 2%; distillation test, boiling point, and oil content measurements. Analysis is done once per batch.
Heavy Benzene: d^20 = 0.91–0.98; initial boiling point ≥ 160°C; distillation yield before 200°C ≥ 60%; boiling point in distillation test; distillation yield before 200°C and specific gravity measurement. Analysis is done once per shift.
Chapter 2: Operating Procedures for Refined Benzene
Section 1: Safety Procedures for the Washing System
(a) Preparations before starting up the system. 1. Drain the water from the unprocessed mixed mixture tank and take a sample for distillation testing. 2. Check that all equipment, pipelines, valves, instruments, and the entire washing system are in good condition and operating properly. The vent valves of equipment such as reactors, alkali oil separators, and stripping units should be closed, while the feed valves should be open. Rotate the couplings of each pump and apply lubricant. 3. Check the levels in each storage tank and prepare diluted alkali. 4. Fill the acid and alkali tanks to capacity. (II) Commencement of work. 1. Start the feed pump to feed material into the feed tank. 2. When the level in the raw material sump is at 1/2. Start the washing pump by first opening the acid valve. Open the oil valve again. After the washing pump reaches normal flow rate, the amount of acid added should be higher at first. After meeting the requirements, it is gradually adjusted to the normal ratio. 3. Once the reactor is filled with oil, start adding water. 4. When the acid oil separator is full of oil, open the alkali addition valve to add alkali, and at the same time start discharging a small amount of waste acid into the regenerated acid sedimentation tank. 5. When the alkali-oil separator is at full flow, oil flows automatically into the washed intermediate tank; the entire washing system operates, and the start-up process is completed. (III) Normal production operations. 1. Regularly check temperatures and pressures in various areas, and adjust the flow rates of the feed pump, washing pump, as well as acids, bases, and water to maintain stable production. 2. Regularly check the levels of raw materials, acids, and bases in the storage tanks to prevent interruptions in the supply of these substances. 3. Emission of waste acid and acid tar. The waste acid and acid tar from the acid oil separator are discharged every two hours; stop discharge once oil is detected. The regenerated acid is discharged into the regenerated acid sedimentation tank, while acid tar can be directly discharged for distillation; however, when it cannot be properly separated from the regenerated acid, it should also be sent to the regenerated acid sedimentation tank for separation. 4. Acid tar treatment: Acid tar is discharged from the acid and oil separator into the stripping unit; the acid tar separated in the regenerated acid sedimentation tank also flows into the stripping unit. The stripping unit processes acid tar once per shift, neutralizes it with waste alkali or fresh alkaline solution, and then heats it using direct steam. The acid tar is required to be neutralized to an alkaline state; regenerated benzene is removed through distillation (with a top temperature of 95°C), the residue contains less than 2% benzene, and then the waste liquid is discharged into the underground tank for acid tar storage. 5. Waste alkali discharge: The waste alkali is discharged intermittently into the stripping tank as indicated by the interface. 6. The interface of the regenerated acid in the regenerated acid sedimentation tank is strictly controlled at 0 above the full-flow level of the acid tar. Under 5 meters, to prevent regenerated acid from entering the stripping process. 7. Treatment of waste alkali: During the operation, any remaining waste alkali is continuously discharged into the acid-base distillation tank, where it is distilled and removed using direct steam. (IV) Suspension of work. 1. Once the treatment of the raw material in the uncleaned tank is complete, stop the raw material pump. 2. After the material in the raw material sump has been processed, first close the oil valve of the washing pump, then close the acid valve, followed by stopping the washing pump and closing the reactor outlet valve to cease adding water. 3. Drain the waste acid and acid tar from the acid oil separator. 4. Open the valve to force all the oil in the acid oil separator out, then stop adding alkali or water. 5. Drain the waste alkali from the alkali oil separator, then continue adding water; once all the oil in the alkali oil separator has been pushed into the washed mixture tank, stop adding water. 6. The remaining oil in the reactor is subjected to blow-off treatment. 7. After the blowing and steaming treatment is completed, the system must be vented; no material should remain inside. 8. Empty all equipment such as the acid oil separator and the alkali oil separator. 9. Stop supplying heating steam to the alkali holding tank and the raw material holding tank. Temporary shutdown: If washing cannot continue due to certain reasons and the shutdown is short-term (48 hours), the oil, acid, water, etc. in the entire system will cease to function. The waste acid in the acid-oil separator, such as acid tar, must be completely drained to prevent tar from clumping together. After draining, it should be emptied again after one hour, as more acid tar will settle in the subsequent feed. In winter, when there is a temporary shutdown, normal shutdown procedures must be followed, that is, all equipment needs to be emptied. Temporary shutdown: If washing cannot continue due to certain reasons and the shutdown is short-term (48 hours), the oil, acid, water, etc. in the entire system will cease to function. The waste acid in the acid-oil separator, such as acid tar, must be completely drained to prevent tar from clumping together. After draining, it should be emptied again after one hour, as more acid tar will settle in the subsequent feed. In winter, when there is a temporary shutdown, normal shutdown procedures must be followed, that is, all equipment needs to be emptied. Precautions: 1. When unloading and transporting acids and bases, it is essential to follow the operational procedures strictly and wear protective equipment to ensure safe production. 2. The indirect steam pressure used in the acid tar stripping kettle must be strictly controlled within 0.2 MPa. 3. The liquid level in the regenerated acid sedimentation tank must be carefully controlled to ensure that waste acid does not enter the distillation vessel, and to prevent acid tar from entering the regenerated acid storage tank. 4. For the steam blowing operation, water should first be passed through the condenser cooler, after which heating should be carried out gradually to ensure that the steam blowing tank is at atmospheric pressure or a stable positive pressure, thereby preventing benzene vapor from escaping and causing poisoning. 5. Try not to make large adjustments to the washing flow rate; instead, adjust it gradually according to production conditions in order to maintain balance in the operation of the distillation system. Section 2: Safety Technical Regulations for Distillation Systems (II) Startup and Shutdown Procedures for the Two Benzene Towers 1. Preparations before startup: (1) Check whether there is water in the crude benzene tank, and drain all the water. (2) Notify the instrument technician in advance to inspect the instruments and check whether all equipment is in good condition and meets the requirements for operation. (3) Open the valves for the condensation cooling water in the diphenyl tower system. (4) Press the oil-water separator to 1/3 of the level gauge height. (5) Close the oil-water separator vent valve and the bottom reboiler vent valve. (6) The steam pipeline discharges condensate water. 2. Commencement of operation: (1) Start the feed pumps for the diphenyl towers, and open the steam valves of the feed heaters in these towers; the crude benzene is then heated before entering the diphenyl towers. (2) When 1/3 of the material is accumulated at the bottom of the tower, indirect steam is turned on, while direct steam is used for gradual heating and blowing. (3) The feed rate should be low at the beginning; once the temperature at the bottom of the tower reaches the specified value (145–155°C) and the heavy benzene meets the required standards, the valve for extracting heavy benzene from the bottom of the tower can be opened to allow its discharge. (4) When the oil level in the reflux column reaches a certain height (400 mm from the oil outlet), start the reflux pump to introduce a small amount of fluid back into the tower, thereby stabilizing the reflux rate and controlling the vapor pressure at the bottom of the tower, as well as maintaining the liquid level in the reflux column. (5) While ensuring the appropriate temperature at the bottom of the tower (by adjusting it using the vapor from the reboiler at the bottom), gradually adjust the feed rate and reflux rate to their normal values. (6) Determine the tower top temperature based on the mass of light benzene, and decide on the level of reflux or whether to turn it on or off. 3. Shutdown: (1) Close the outlet valve of the crude benzene tank, stop the feed pumps for the two benzene towers, and then close the steam valve of the feed heater. (2) Close the bottom of the tower heavy benzene extraction valve, then close the reboiler steam valve. (3) Stop the backflow into the tower; use water pressure from the reflux column of the oil-water separator to force all the light benzene into the light benzene storage tank. (4) Open the device vent valve to vent the device. (5) Close the cooling water valves of the diphenyl tower system. Temporary shutdowns: When production cannot continue for some reason and the shutdown duration is short, a temporary shutdown is carried out. In accordance with the requirements for such shutdowns, the entire system is brought to a stop, but the oil-water separator is not pressurized with water and the equipment is not emptied. (III) Startup and shutdown operations of the initial distillation tower: 1. Preparatory work before startup. (1) Allow the light benzene storage tank to drain naturally. (2) Notify the instrument technician in advance to inspect the instruments and check whether all equipment is in good condition and meets the requirements for operation. (3) Close the equipment vent valves, close the valve allowing the mixture to flow into the uncleaned tank, open the valve for the initial distillate, and open the valve for sending the mixture to the light benzene storage tank. (Note: When the untreated fraction and the initial distillate are unsatisfactory, no extraction is carried out in the cycle. ) (4) Open the cooling water valve of the initial distillation system. (5) Pre-pressurize water in the initial distillate oil-water separator (1/3 of the water level gauge is sufficient). (6) The steam pipeline discharges condensate water. 2. Driving: (1) Start the feed pump for the initial distillation tower and adjust the feed rate. (2) When the material accumulation at the bottom of the tower is 1/3, open the heater steam valve and gradually heat it to around 93°C. (3) When the reflux column reaches a certain height (above 400 mm from the oil outlet), start the reflux pump to feed the reflux liquid into the tower and stabilize the reflux rate. Control the indirect vapor pressure. The above over-stability is a cycle. After 4 to 6 hours, the entire tower becomes stable; the temperature of the five trays is between 88% and 92%. An analysis of the mixture is conducted – if the drip point of this mixture is greater than 82°C, and the amount distilled from the initial fraction at temperatures above 80°C is sufficient, then the circulation can be stopped. (4) Open the valve leading to the unprocessed tank for the mixed mixture, close the valve leading to the light benzene tank, and open the valve leading to the distillate tank for the initial distillate. (Generally, the initial distillate is not required either at the beginning of operation.) (5) The extraction of the initial distillate is determined by the tower top temperature; when the tower top temperature is below 60°C, forced extraction should be carried out in an appropriate amount, and it is not allowed to allow the liquid to flow back completely to the light benzene tank. When the tower top temperature is above 60°C, extraction is not permitted, and the flow rate should be adjusted by allowing the liquid to flow back completely temporarily. 3. Parking: (1) Open the valve for sending the mixture to the light benzene tank, and close the valve for sending it to the unprocessed tank. (2) Close the outlet valve of the light benzene tank, stop the feed pump for primary distillation, and close the heating steam valve of the reboiler. (3) Stop the reflux to the tower; use water pressure in the reflux column of the oil-water separator to send all the initial distillate to the initial distillate tank, and then stop the reflux pump. (4) Open the device’s vent valve to completely drain the device. (5) Close the cooling water valve of the initial distillation system. (6) Record the tower shutdown time and venting conditions. 4. Intermediate cycle in case of temporary shutdown: When it is not possible to continue discharging material due to certain reasons, the cycle can be repeated or a temporary shutdown can be implemented. (1) If discharge cannot be achieved after a short period of cyclic operation, follow the cyclic process procedure used at startup. (2) Temporary shutdown: If it takes a long time to resolve the fault, a cyclic transition method should not be used; instead, the entire system should be shut down as required for shutdown, but the equipment should not be emptied, and there is no need to press water into the oil-water separator or the reflux column. (III) Startup and shutdown operations of the benzene stripping tower. 1. Preparatory work before starting up: (1) Drain the mixed water from the tank to make it clean. (2) Notify the instrument technician in advance to inspect the instruments. Check whether all equipment is in good condition and meets the requirements for operation. (3) Contact the washer to add fresh alkali solution to the circulation alkali oil separator up to 2/3 of the liquid level gauge, open the outlet valve for the circulation alkali, and start the circulation alkali pump. Under normal operation, fresh alkali solution should be replaced when the alkali concentration is <4%. (4) Open the cooling water valve of the benzene blowing tower system. (5) Close the oil-water separator and reboiler vent valves, and open the bottom of the tower slag discharge valve. (6) Steam pipes drain condensate water. 2. Startup: (1) Start the feed pump for the benzene-blowing tower, and open the heating steam valve of the evaporator. The washed mixture is first heated to 105–115°C in the evaporator before being fed into the benzene-blowing tower. (2) When there is material accumulated at the bottom of the tower, use direct heating steam for blowing, while simultaneously activating the indirect steam heating system located inside the bottom of the tower. (3) The feed flow rate should be low at first to ensure that the temperature at the bottom of the tower and the slag are free of oil, after which the flow rate can be gradually increased back to normal levels. 3. Shutdown: (1) Stop the feed pump of the benzene tower, and then close the heating steam valve of the evaporator. (2) Reduce the direct steam supply, then open the slag vent valve to discharge the slag at the bottom of the tower into the benzene residue tank; after discharge is complete, turn off the direct steam supply. (3) Stop the circulating alkali pump, and use pressurized water to push the oil in the alkali oil separator into the underground drain tank. (4) Drain the circulating alkali tank. (5) Close the main water valve of the benzene blowing system. Temporary shutdown: If the benzene stripping tower is unable to continue operating for some reason, but the shutdown duration is short, a temporary solution can be adopted – that is, stop feeding material, cease heating the evaporator and the tower, introduce steam at the bottom of the tower and vent from there; no need to vent other equipment. (IV) Startup and shutdown procedures for the benzene tower, toluene tower, and xylene tower: 1. Preparatory work before startup: (1) Check whether the equipment in the system is in good condition and meets the requirements for startup. (Pipes, valves, instruments) (2) It is necessary to remove any water from the benzene tank, the pure benzene residue tank, and the toluene residue tank; the water must be completely drained. (3) Close the equipment vent valve, open the system water valve, and fill the oil-water separator to 1/3 of its liquid level. (4) Open the residue at the bottom of the tower. The tower top product is returned to the pure benzene feed tank; the start/stop valve for that tank is opened. (5) Drain condensate from steam pipes. 2. Commencement of operation: (1) Start the feed pump to supply material into the tower and adjust the flow rate accordingly. (2) When 1/3 of the material is remaining at the bottom of the tower, open the reboiler steam valve to heat gradually. (Note: Direct steam should be introduced to the dimethyl tower gradually once it has reached a stable temperature.) (3) When the oil level in the oil-water separator reaches a certain height, start the reflux pump; the reflux liquid is then fed into the tower to maintain stable reflux. (Note: The reflux pump should be started in the dimethyl tower when the oil level coming in for reflux exceeds 400 mm above the outlet.) (4) Adjust parameters such as the feed rate and the amount of indirect steam (including direct xylene steam) to ensure stable operation of the tower; the product is taken out before the product pump and flows into the raw material tank via the oil-water separator, while the residual oil at the bottom of the tower is also returned to the tank used for starting up or shutting down the process. The above process is a cyclic overshoot; after 4–8 hours, the operation of the tower will stabilize. When the temperatures at the top and bottom of the tower reach the specified operational values, a sample can be taken for analysis; if the product meets the required standards and the residue at the bottom of the tower also complies with the emission regulations, then the circulation process is completed. (5) Transfer the product to the product tank, drain the residual oil to the raw material tank for the next cycle (next distillation), and drain the dimethyl residue to the dimethyl residue tank; close the valves for the residual oil and product return lines as well as those for starting and stopping the process. 3. Parking: (1) Return the residual oil at the bottom of the tower to the original start/stop tank. (2) Turn off the heating steam and stop the feed pump. (3) Stop the recirculation pump. (4) Press water into the reflux column of the oil-water separator to force all the oil into the product tank (water pressure is not necessary if the shutdown time is not too long). (5) Open the bottom valves of the tower as well as the vent valves of equipment such as the oil-water separator, to drain all the remaining oil from these devices. (6) Close the system cooling water valve. If this system is unable to continue operating for some reason, it can run in the cycling mode as when it was started up. Section 3: Causes of Common Problems and Solutions (I) Washing Section: 1. The washed mixture does not meet the quality standards. Reasons: (1) Moisture in the raw materials. (2) Imbalance in the flow ratio of acid and base. (3) Concentration reduction: Treatment method: Empty the washed tank ； 2. Acid cannot be added. Reasons: (1) The acid sump is empty; (2) The acid delivery pipeline is blocked. Solutions: (1) Add acid to the acid sump; (2) Clean the pipeline; (3) If acid still cannot be added after 5 minutes, carry out a temporary shutdown. 3. Alkali cannot be added: Reason: Same as why acid cannot be added. Treatment: If the alkali still cannot be added after 15 minutes, temporary shutdown is initiated. 3. The oil temperature behind the reactor rises suddenly. 　　　Reason: (1) Moisture in the raw material 　　　　　 (2) Sudden change in the raw material composition. Action: Check for the above reasons. 4. Acid tar formation is caused by a low initial boiling point of the raw materials, as well as high bromine value and CS2 content. Action: Contact the distillation operator to increase the frequency of acid tar discharge. (II) System section: 1. Sudden power or water outage – Action: Immediately stop heating and shut down the system temporarily. The equipment does not need to be emptied. 2. Steam supply interruption: Handling: Implement a temporary shutdown; for towers that cannot operate properly due to a drop in steam pressure, they can be switched to the startup cycle or placed on temporary shutdown. 3. Compressed air interruption: Handling: Immediately use manual valves to shut off the automatic control valves and stop using the instruments. If normal operation is disrupted, the system can be switched to the startup cycle before making adjustments; in severe cases, a temporary shutdown may be necessary. 4. Oil leakage from the condenser cooler drain pipe. Causes: (1) Water supply interrupted or insufficient water volume. (2) The reflux or feed rate is too low. (3) Freezing in the pipeline after the primary distillation condenser for pure benzene. (4) Blockage in the pipes after the condenser: Check whether the cooling water volume, as well as the feed and return flow rates, are normal. 5. The feedstock or reflux pump stops operating suddenly. Raw materials: Electrical problems. Solutions: (1) Replace with a backup pump and adjust to normal operation; (2) Reduce the amount of direct or indirect steam used; (3) Switch to circulation mode when the tower temperature rises; (4) Shut down the tower promptly in severe cases. Chapter 3: Safety Technical Regulations for the Benzene Refining Workshop Section 1: General Provisions 1. The benzene products produced in the benzene refining section are highly prone to causing fires, explosions, and poisoning incidents. Therefore, all staff members must be familiar with the safety regulations and adhere to them strictly. 2. For safety technology work, it is necessary to mobilize and organize employees so that everyone is involved in safety efforts, thereby eliminating potential hazards for accidents at their earliest stage. 3. Safety technology work must be given high priority in terms of mindset and included in the work agenda; it should be planned comprehensively to ensure that this work is carried out effectively. Ensure the normal progress of production. 4. After any accident, large or small, it is necessary to organize the personnel on duty to investigate the causes, draw lessons from them, and establish measures to prevent such accidents from occurring in the future. 5. Smoking is prohibited in areas where smoking is forbidden. 6. All employees of Jingben should be familiar with the fire alarm number, as well as the phone numbers of the security department and the health clinic. 7. All staff at Jingben must keep in mind that our workshop is a class-1 flammable and explosive area, and they should give top priority to safety over production tasks. Section 2: Technical Regulations for Production Safety 1. All new workers must undergo three levels of safety training provided by the company, as well as the workshop and production team, and only after passing the examinations are they allowed to enter the production areas. 2. Visitors from outside the company must obtain approval from the relevant department of the company before they can enter the site. 3. External visitors and trainees must undergo safety training before they can enter the production area. 4. All personnel in this work area, as well as visitors from outside, are prohibited from wearing shoes with nails or carrying any flammable items (such as lighters, matches, etc.) into the production area. 5. All personnel in this section must keep the fire alarm phone number and the procedures for reporting fires in mind. 6. All operators in this section must wear all necessary personal protective equipment before entering the site. 7. All operators in this section are prohibited from placing oil-soaked rags on the steam pipes or using benzene-based substances for cleaning the floors. 8. When motor vehicles enter the benzene purification site, fire prevention measures must be taken and approval from the relevant authorities is required. 9. All equipment and pipelines in this section shall be equipped with grounding and lightning protection devices to prevent lightning strikes and static discharge. 10. The lightning protection system must be kept in good condition; a thorough inspection must be carried out each year in conjunction with the relevant higher-level authorities, with records to be kept. 11. The vent pipes and flame arresters of each storage tank must be kept in good working condition. 12. It is prohibited to use iron measuring tapes to measure the volume of storage in various tanks; only non-ferrous metal or wooden measuring tapes are allowed. 13. No items are allowed to be placed in the various passages within the work area; they must remain unobstructed. Nothing that could hinder operations shall be kept inside the factory building. 14. For the operating equipment in this section, non-explosion-proof motors are prohibited; explosion-proof lighting fixtures must be used, and temporary lights are not allowed. 15. Equipment such as steam, fire extinguishing, and foam systems must be kept in good condition; they should be tested once per quarter, and all personnel must be able to use fire extinguishing equipment skillfully. 16. Operators in this work section who enter equipment with high concentrations of benzene vapor must wear gas masks, and at least two people should be present. 17. It is prohibited to expose sampling bottles containing benzene to direct sunlight, as well as to use benzene for washing hands, utensils, and clothing. 18. It is prohibited to use metal tools to strike equipment in this area; to avoid the generation of sparks, all tools used here must be made of non-ferrous metals, or if iron tools are used, they must be painted yellow. 19. If the skin is burned by acids or bases, it is prohibited to use neutralization; instead, it must be rinsed with plenty of water. 20. When adding acids, bases, and feed materials, one must not leave the site to prevent accidents caused by a full tank. 21. The warning safety signs hung on site must not be moved arbitrarily. 22. When diluting sulfuric acid, water must be added first and then the acid; it is strictly forbidden to pour water into the acid. Section 3: Safety and Fire Prevention Technical Regulations 1. Fire prevention and extinguishing: Fire prevention: (1) Welding and other similar operations are prohibited in all areas except those designated for such purposes; if such operations must be carried out, the necessary procedures must be followed. (2) Flammable materials, hazardous substances, and various types of oils must be stored in designated locations, with a dedicated person responsible for their supervision. (3) It is prohibited to use oilcloths, paper, and flammable materials to dry things over radiators, steam pipes, or heated equipment. (4) Each production facility should be equipped with adequate ventilation to keep the flammable gases inside at levels below the explosive range. (5) The grounding wires of various equipment and the static electricity protection devices of pipelines should be inspected regularly. Inspect twice a year and keep records. (6) The fire hydrants in the workshop should be regularly inspected and protected from freezing. (7) All fire-fighting equipment at each post should be under the responsibility of a designated person to ensure it remains in good condition. In the event of damage or loss, report it promptly for repair; regular inspections must be carried out, and fire protection equipment must not be used for other purposes. (8) The equipment used for foam suppression must be unobstructed, and a dedicated person should be assigned to conduct regular inspections. Fire extinguishing: (1) In the event of a fire, call to inform the relevant supervisors within the company as well as the appropriate departments. (2) In the event of a fire, stop the vehicle immediately and mobilize personnel to extinguish it. (3) After the fire is extinguished, a dedicated person should inspect the site to completely eliminate any sources of fire. (4) After the fire is extinguished, clean the fire-fighting equipment, return it to its original place, and replace any items that have been used. 2. Hot work regulations: (1) Any work involving open flames in areas not designated for such work requires a hot work permit. (2) Once the hot work permit is approved, it must not be altered; it must be carried with one at all times for inspection. 3. Explosive limits of flammable substances (%): (1) Carbon monoxide: upper limit of 75, lower limit of 1.28. (2) Carbon dioxide: upper limit of 5, lower limit of 1.28. (3) Pure benzene: upper limit of 6.75, lower limit of 1.31. (4) Toluene: upper limit of 6.75, lower limit of 1.27. (5) Xylenes: upper limit of 6, lower limit of 1.0. Section 4: Safety and Health Technical Regulations 1. Permissible concentrations of hazardous substances: (1) The maximum allowable concentration of oxygen in indoor air is not more than 0.03 milligrams per liter. (2) The maximum allowable level of carbon monoxide in indoor air is not more than 0.03 milligrams per liter. (3) The maximum allowable concentration of carbon disulfide in indoor air is not more than 0.01 milligrams per liter. (4) Indoors or within equipment, the maximum allowable concentration of pure benzene in the air is not more than 0.04 milligrams per liter. (5) Indoors or within equipment, the maximum allowable concentration of toluene in the air is not more than 0.1 milligrams per liter. (6) Inside indoor equipment, the maximum allowable concentration of xylene in the air shall not be less than 0.1 milligrams per liter. 2. Occupational health: (1) The production facilities should be cleaned regularly to maintain cleanliness. (2) In all production workshops equipped with ventilation systems, the ventilation should be turned on 10–15 minutes before starting work; the exhaust fans should be activated first, followed by the supply fans. (3) Sufficient lighting should be provided at passages, safety doors, safety ladders, etc. (4) It is prohibited to heat lunch boxes on production equipment, and it is forbidden to eat in areas with toxic substances or dust; hands must be washed before eating. (5) It is necessary to wear protective equipment appropriate to the nature of the work before starting work. Chapter 4: Commissioning Plan for Pure Benzene Section 1: Pneumatic Pressure Testing of Pure Benzene Pipelines 1. Pneumatic pressure testing of pure benzene pipelines. (Air or steam pressure testing is both acceptable.) (I) Purpose of pressure testing: 1. To check through pressure testing whether equipment, pipelines, welds, flanges, etc., are airtight, so that any defects can be identified and corrected in a timely manner. 2. By conducting pressure testing, conditions are prepared for subsequent commissioning and operation, while also enabling operators to become more familiar with the equipment and its interconnections. (II) Pressure testing preparations: 1. For the feed pipes of each tower, a pressure test pressure of 5 kg/°C·m² is used. 2. For the reflux pipes of each tower, a pressure test pressure of 5 g/cm² is used. 3. For the vapor pipelines from the condenser to the tops of the towers, a pressure test pressure of 5 K/°C·m² is used. 4. For the oil-water separator, a pressure test pressure of 15 kg/°C·m² is used. 5. For the pipelines from the washing mixing pump to the alkali-oil separator, a pressure test pressure of 5 kg/°C·m² is used. 6. For the pipelines carrying concentrated acid, a pressure test pressure of 5 kg/°C·m² is used. (III) Pressure testing: 1. Connect the temporary gas pipes properly. 2. Prepare several temporary pairs of rubber hoses. 3. Prepare an adequate number of flange gaskets and blind plates in various specifications, as well as wire. 4. Prepare pipe ends and pressure gauges of different specifications. 5. Prepare a notebook for recording defects. 6. Before pressure testing, all equipment pipes, valves, safety devices, etc. should be thoroughly inspected to ensure that no blind flanges remain in place. 7. Perform closing tests on all valves in the piping system and pumps to check their flexibility. 8. Cooperate well with the testers; assign specific personnel to each area to carry out inspections, keep records, and address issues one by one. 9. Pressure testing must be carried out before the equipment pipes are insulated. 10. Before pressure testing, first open the valves of the pipes in each device and use gas to clean them, removing any dirt and accumulated water inside the devices, before closing the valves. 11. The pressure and airtightness testing of individual units shall be carried out by the construction unit and relevant departments (before conducting pipeline pressure testing, all records related to pressure testing must be collected thoroughly as one of the bases for putting the installation into use). (IV) Pressure testing methods: 1. Each oil-water separator system should be tested as a single integrated unit, that is, as one complete device. (1) Install a blind plate at the outlet of the condenser. (2) All the vent valve at the bottom of each oil-water separator, as well as the reflux extraction valves, shall be completely closed. (3) Attach a temporary gas pressure regulator using a rubber hose and a pressure gauge to the glass level gauge of the oil-water separator. 2. Raw material pump and reflux pump systems: (1) Blind flanges should be installed at the inlet and outlet of each pump to prevent dirt from entering the pumps. (2) Check the pressure at the pressure gauge on the pump outlet pipe. (3) Clear the pipeline by blowing air through it; once the pipeline is cleared, adjust all valves to the following positions: A: Close the suction valves at the bottom of each raw material tank. B: Close the return suction valve for each clutch. C: Close the valves on the feed pipes of each tower. d: Close the valves of each reflux tube. E: Open all the piping for the pumps (without using the control valves on the instruments). 3. Washing system: (1) The pipelines from the outlet of the raw material storage tank and the outlet of the concentrated acid storage tank to the inlet of the mixing pump, as well as the pipeline from the outlet of the mixing pump to the inlet of the reactor, constitute one pressure testing system. A: First, clean the pipeline with gas and then conduct a pressure test. B: The gas passes through a bypass pipe, without going through the pump body. C: Gas bypasses the rotameter, not passing through it. (To prevent internal leakage of the valve and damage caused by gas entering the flow meter, the flange at one end of the single flow meter can be opened.) (2) The pipeline from the reactor outlet to the acid oil separator inlet constitutes a pressure testing unit. Gas does not flow through the rotameter. Section 2: Trial Run of Pure Benzene Trial Run of Pure Benzene: (I) Purpose of the trial run: 1. Through the trial run, to check whether the equipment, pipes, valves, as well as the welds and flanges are airtight, and whether the valve actuators operate smoothly. 2. Check for defects in the equipment during operation to facilitate correction. 3. Observe and adjust to ensure that various control instruments operate accurately and flexibly. 4. Check that all pipelines are installed properly and unobstructed. 5. Through trial operation, the operators become familiar with the operation of the equipment, improving their proficiency in handling it; they also learn about the location of the equipment, pipes, and valves as well as their performance characteristics. Additionally, they understand the interconnections between different positions, thereby laying a foundation for full-scale production. (II) Test run projects. 1. Feed pump for distillation 2. Reflux pump for distillation 3. Discharge pumps for various products and by-products. 4. Two benzene towers, distillation tower, benzene blowing tower, neutralizer, pure benzene tower, xylene tower, etc. 5. Condensers, coolers, reboilers, etc. 6. Oil-water separators and alkali-oil separators, etc. 7. Various pipes and pipe fittings. 8. Instruments for indicating, recording, and regulating various temperatures, flow rates, pressures, and material levels. 9. Washing system. 10. Fire protection system (water, steam, foam). (III) Test conditions: 1. All equipment must be fully installed, and safety devices must be complete. 2. Before testing, all equipment and pipelines must pass pressure tests before testing can proceed. 3. Before testing, the interior of the factory building, the area around the equipment, as well as the inside of the equipment and pipes must be cleaned. 4. Before the test run, ensure that all necessary tools, materials, spare parts, as well as the records and forms required for the test run are ready. 5. Conduct a trial run before insulating the equipment pipes. 6. Contact the workshop scheduler and request that the suppliers of water, electricity, gas, and air ensure timely and adequate supply. 7. The instruments have been installed and calibrated successfully. Requirements: (1) Medium-pressure steam pressure: 8–10 kg/Cm²; (2) Cooling water pressure: 3–5 kg/Cm²; (3) Voltage: 380 V; (4) Air pressure: 5 kg/Cm² (to ensure sufficient air for instruments). (IV) Commissioning of the pure benzene distillation system: 1. Method of commissioning: (1) Test each tower’s system by circulating water. (2) The steam pipeline is purged with steam, and steam is introduced for inspection. (3) After the steam testing of the equipment in each unit is completed, a coordinated trial operation is carried out. (4) Distillation coordination system: Conduct a coordinated trial operation in accordance with the normal production sequence. 2. Trial operation criteria: (1) Time: Each oil pumping pump shall operate continuously and normally for 4–8 hours; the total trial operation time for this system is 3 days (to achieve stability). (2) Equipment operation criteria: A. Raw material pumps and return pumps: The temperature of each bearing in the pumps shall not exceed 60°C; the temperature of the motors shall not rise by more than 50°C. There shall be no leaks from the packing glands (or mechanical seals). The pumps and motors must not experience friction or vibration, and there shall be no oil leakage or splashing from the lubrication parts of the bearings. B. Each distillation tower: The tower body, as well as all associated pipelines, flanges, and valves, must not leak. The bubble formation on the tower trays shall be proper. C. Each separator: The main body and all pipe connections must be leak-free; water testing should be conducted at each sampling port. D. Condenser and cooler: The main body and all pipe connections must not leak. F. All instruments must be accurate and in good working condition. 3. Commissioning operations: (1) Preparations before commissioning A. The operator shall check whether the equipment within this system has been cleaned properly. B. Check whether the lubrication parts of the moving components of the equipment have been lubricated. C. The electrician should inspect the relevant electrical equipment and prepare to supply power. D. Check whether the water supply and steam pipelines are unobstructed. E. Use steam to check whether the suction and discharge ports of each pipeline pump are unobstructed, paying special attention to any pipes that may be blocked by blind plates. F. Check whether the safety devices are complete and whether the equipment is properly grounded. G. Check the temperature, pressure, flow rate, level of the metering system, as well as whether all the instruments are properly installed and complete. H. It is necessary to specifically inspect the various piping systems and the accessories associated with the pumps, to check whether the valve closing tests are performed smoothly. I. Prepare all kinds of tools and lubricants (in addition to the regular tools, each post has two “F” shovels). J. All devices are in working condition. (2) Operation steps: A. First, conduct a system trial run for the two benzene towers. B. Prepare all power sources. C. Supply direct steam to the tower to maintain a pressure of 0.5–0.8 kg/Cm^2 inside it. D. Add water to the oil-water separator. E. Temperature, level, pressure, and instrument operation. F. Reduce the reflux flow rate and conduct a bubbling test on the tray. H. Fill the heavy benzene storage tank with 40–50 tons of water, and open the valve of the lower pumping pipe. i. After the tray bubbling test is completed, start the feed pump to supply water into the distillation tower. It circulates through the cooler to the heavy benzene storage tank, while the raw material flow meter is put into operation. J. Start with a small dose, then gradually increase it to the maximum amount. K. When the feed pump meets the requirements, stop feeding from the top feed pump and start the return pump; the circulation method remains the same. L: The amount of water fed into the tower must be equal to the amount discharged, in order to maintain the liquid level inside. For M and other types of oil leaks, they can be cleaned using steam or made pressure-resistant once the inspection is successful. N. Commissioning operations for the other towers, modeled after the diphenyl tower. 5. Procedures after the vehicle owner parks the vehicle: A. Vehicles can be parked one after another once the test driving meets the requirements and the allotted time has passed. B. Stop the steam. C. Stop the feed material and the reflux pump. D. Drain the pumps inside the tower and the storage tank. E. Remove the inlet and outlet pipes for the feed material and the reflux line, and drain them completely. F. Remove all temporary pipes and install the permanent pipes properly. (5) Commissioning 1. Commissioning methods: (1) Commission the acid-base tanks, pump systems, and water used in the scrubber. (2) The various sections of the steam pipes, as well as the steam blowdown system, are cleaned using steam. 2. System for testing: (1) Water testing system: 3. Testing criteria: (1) Each pump should operate continuously for 8 hours. (2) The shaft temperature of the pump must not exceed 60°C. (3) The motor temperature rise shall not exceed 50°C. (4) The gland packing (or mechanical seal) of the pump must not leak. (5) There should be no sound of metal friction or vibration of the motor in the pump. (6) The bodies of each device shall remain leak-free. (7) All pipes and fittings shall be kept leak-free. (8) The instruments are accurate and easy to use. 4. Commissioning operations: (1) Check whether the interiors of all pipes are clean and unobstructed. (2) Check whether the electrical equipment is in good condition and inspect the grounding wires of the equipment. (3) Check whether all instruments are present. (4) Check whether all sampling points are fully equipped. 5. Commissioning steps: (1) Fill the uncleaned tanks in the oil depot with 30 tons of water, and fill the acid, alkali, and underground tanks with water. (2) Start the raw material pump and the pump for transferring concentrated acid solution; once there is a sufficient liquid level in the alkali preparation tank, start the pump located at the bottom of that tank. At the same time, water should be added to the high-level tanks containing the raw material acid and alkali. (3) Once the 3 high-level tanks are full of water, start the acid washing mixing pump to supply water to the mixing tank; from there, the water flows through the reactor water mixer, the acid-oil separator, the alkali addition mixer, and the alkali-oil separator, eventually reaching the washed mixture tank. (4) Adjust the flow rate of each circuit as required. 6. Post-parking procedures: (1) All water remaining in the equipment and pipelines must be completely drained into the sewer system. (2) The water stored in the oil tank is pumped out for inspection, and rust and debris are removed. (VI) Commissioning of the finished pumps and products, as well as the by-product tank system. 1. (1) Fill each storage tank with water for trial operation. (2) Piping and steam pipes are purged and cleaned with steam. 2. Testing system: Product injection system, auxiliary product tank pump. 3. Testing criteria: (1) There should be no grinding noises inside the pump during operation. (2) The storage tank itself must not leak. (3) There are no leaks at the joints of various pipes, nor at the valves, etc. 4. Commissioning operations: (1) Preparations before commissioning: A. Inspect and clean all equipment systems. B. Check whether lubricant has been added to each pump. C. Check whether the safety devices in all areas of the oil storage tank area are in good condition, including grounding. (2) Commissioning steps: A. A certain amount of water should be added to each oil storage tank, and the valves of the lower pumping pipes should be opened. B. Start the finished pump to draw water, and then return it to the large tank for circulation. (3) Handling after parking: A. Drain all the water from the tank, conduct an inspection, and remove rust and debris. B. After all the piping systems have been drained, close the valves. (4) Fire system testing 1. Testing method: A. For steam fire extinguishing, testing is carried out directly using steam. B. Water test of the foam fire extinguishing system. 2. Commissioning criteria: A. No leakage in pipes and fittings. B. The pump is operating correctly with no abnormal noises. C. The steam pipes are unobstructed, and there is no internal leakage in the main steam valves. Chapter 5: Responsibilities for the Benzene Purification Post 1. Responsibilities of the Workshop Director: 1. Obey superior instructions and organize the production management of the entire workshop. 2. Responsible for organizing the entire workshop to complete various tasks assigned by the company or branch factory. 3. Responsible for implementing the economic responsibility system within the workshop. 4. Responsible for ensuring the implementation of rules and regulations as well as labor discipline within the workshop. 5. Responsible for organizing various labor competitions across the entire workshop. 6. Responsible for safety education, safe production, and civilized production throughout the workshop. 7. Responsible for overall quality management in the entire workshop and organizing equipment maintenance there. 8. Responsible for submitting plans for equipment maintenance, as well as plans for materials and equipment, and for strengthening the control of quotas regarding such equipment and spare parts. 9. Responsible for the political, cultural, technical, and ideological work of all employees in the department. II. Responsibilities of the Team Leader 1. Obey superior leadership and organize the team to complete all production tasks assigned by the entire factory or workshop. 2. Be responsible for ensuring safe and civilized production in the own shift. 3. Responsible for organizing various labor competitions within the class. 4. Be responsible for the quality management of the team, reducing consumption and increasing yield. 5. Responsible for carefully filling out the shift handover records, briefing the incoming crew on the production situation of the current shift, and organizing the timely handover of duties. III. Responsibilities of the washing pump operator. 1. Carry out work under the leadership of the team leader. 2. Master the washing procedures, and be responsible for starting up and shutting down the operation as well as carrying out normal operations. 3. Responsible for the proper operation and maintenance of the equipment, pipes, and valves associated with this position, as well as eliminating any leaks or losses at that location; during the morning shift, responsible for applying lubricant to all pumps. 4. Monitor parameters such as the oil temperature in the vinegar washing tank, the temperature in the dilute alkali tank, pump head pressure, and flow rate; strengthen routine inspections and adjust the operating parameters to stay within the specified ranges. 5. Keep track of the inventory in each tank, and be responsible for the supply of raw materials used for washing, as well as acids and alkalis. 6. Responsible for the management of raw material pumps, washing pumps, regenerated acid pumps, submersible pumps, acid sump tanks, alkali sump tanks, raw material sump tanks, steam stripping condensation coolers, acid tar sedimentation tanks, steam stripping reactors, alkali preparation tanks, acid underground tanks, alkali underground tanks, acid storage tanks, alkali storage tanks, regenerated acid tanks, tanks No. 2, 3, 4, 5, and 6, acid tar underground tanks, waste alkali steam stripping reactors, and waste alkali steam stripping condensation coolers. 7. Responsible for the measurement and recording tasks related to this position. IV. Responsibilities of the Washing Worker 1. Carry out work under the supervision of the team leader. 2. Master the washing operation procedures, be responsible for starting and stopping the washing process, and ensure safe production. 3. Responsible for the maintenance and proper operation of the equipment, pipes, and valves associated with this position. 4. Master the operational parameters for this position, strengthen routine inspections, and adjust any unreasonable parameters. 5. Responsible for the management of acid-oil separators, alkali-oil separators, acid addition mixers, reactors, water addition mixers, alkali addition mixers, steam-blowing oil-water separation units, and various flow meters. 6. Be responsible for the material balance related to washing; before intermittently discharging acid tar, waste acid, and waste alkali, it is necessary to contact the washer pump operator. 7. Be responsible for ensuring safe washing operations and eliminating leaks. In the event of an accident, follow the instructions of the team leader. 8. Keep the work area clean and fill in the operation records carefully. V. Distillation Water Pump Operator: 1. Be familiar with the operating procedures for shutting down the distillation system, work together with the distillation operators to carry out tasks such as starting up and shutting down the system as well as temporary shutdowns; be responsible for pressurizing the oil separator. 2. Responsible for the sampling and testing of various products and intermediate products in the distillation system. 3. Responsible for the maintenance and upkeep of the equipment, valves, and pipelines under his/her responsibility. 4. Responsible for the maintenance, upkeep, and proper operation of the equipment, pipelines, and valves associated with this position, as well as eliminating any issues such as leaks or spills. 5. Responsible for adjusting the water temperature at the outlets of various cooling equipment. 6. Keep the work area clean and fill in the operation records carefully. 7. Keep track of the inventory levels in each system during startup and shutdown processes, work together with the distillation operator to maintain material balance, ensure that the work area remains clean as well as that pumps and motors are kept clean; the person on duty in the early shift is responsible for applying lubricant to the pumps. 8. Responsible for the management of the pumps, all coolers, oil-water separators, and underground storage tanks in the diphenyl system, primary distillation system, benzene blowing system, pure benzene system, methyl system, and dimethyl system. 　9. Master safety knowledge, avoid illegal operations, and ensure safe production. VI. Responsibilities of the Distillation Operator 1. Work under the supervision of the team leader. 2. Master the operating procedures for starting up and shutting down the distillation system, and be responsible for ensuring its normal operation during these processes, as well as addressing issues such as leaks, spills, and other accidents. 3. Responsible for the maintenance of all equipment and valves related to this position. 4. Responsible for operating the circulating alkaline oil separator, and regularly measuring and replacing the alkaline solution. 5. Be responsible for the operational metrics of this system; conduct thorough checks through calls and carry out precise operations. 6. Keep track of the inventory levels at the start-up and shutdown stages of various systems, strengthen communication with the distillation pump operators, and maintain control over the material balance in continuous production. 7. Responsible for controlling the quality of products and intermediate products (semi-finished goods). 8. Responsible for transporting the initial distillate; prior to transportation, coordination with the Chemical Production department is required. Any leaks or spills along the pipelines used for transporting the material outside the Chemical Production facility are the responsibility of the party carrying out the transportation. 9. Responsible for ensuring safe and civilized production at the work site. 10. Responsible for the management of all towers, instruments, and control valves. 11. Fill in the records carefully and on time, and keep the record sheets clean. VII. Post Responsibility System for Oil Depot Workers 1. Work under the leadership of the team leader. 2. Be familiar with the operating procedures for starting up and shutting down the distillation system, and work together with distillation operators and distillation pump operators to carry out tasks such as startup, shutdown, and temporary stops. 3. Responsible for the operation of the entire oil depot during the shift. 4. Be responsible for the drainage of each storage tank, monitor the liquid level in each tank; when the upper or lower limit levels are reached, promptly contact the shift leader or distillation operator to replace the storage tank. 5. Responsible for filling in the oil depot operation records and calculating the material balance for the shift (processing volume, production volume, amounts of materials received and sent, etc.). 6. Must have knowledge of safety procedures, avoid illegal operations, and ensure safe production. 7. Be responsible for tanks No. 1–22, the underground tanks, the control separator, the steam pump, the product transfer pump, as well as the management of all drainage oil seals during shift duty. VIII. Responsibility System for the Finished Pump Operator Position 1. Carry out work under the supervision of the workshop supervisor. 2. Responsible for the maintenance, upkeep, and proper operation of the equipment, pipelines, and valves associated with this position, in order to eliminate any leaks or losses of fluid. 3. Use steam pumps such as centrifuges correctly to transport pure benzene, toluene, xylene, residual gases, dimethyl residues, and heavy benzene. Before transportation, contact the oil depot; the sender is responsible for any leaks, spills, or other losses that occur outside the walls of the oil depot during the transfer of materials. 4. Be responsible for tanks No. 1–22, the underground tanks, the control separator, the product transfer pumps, and the management of all drainage oil seals during shift. 5. Keep the work area clean and fill in the operation records carefully. IX. Post Responsibility System for Duty Personnel: During periods of shutdown, the duty personnel assigned to each shift must carry out handovers on time, remain at their posts, adhere strictly to discipline, be responsible in their work, conduct regular inspections, and ensure the safety of purified benzene; they must also prevent any accidents or incidents from occurring. The specific responsibilities are as follows: (a) Assist the security staff in enforcing the rules regarding access to purified benzene, prohibiting the entry of any kind of ignition sources. (b) Responsible for campus safety and handling various matters on campus on an ad-hoc basis. (c) Responsible for the management of items and tools throughout the workshop. (d) Responsible for making regular inspections of the liquid level changes in various storage tanks as well as the condition of other equipment. (e) Explain in detail to those leaving work the situations that occurred in the shift and the methods taken to handle them. (f) Be responsible for carefully filling out various records and shift handover records. X. Post Responsibility System for Personnel Guarding the Benzene Processing Area 1. All personnel from the benzene processing workshop are prohibited from entering the area without the approval of both the company and the workshop. 2. Unapproved outsiders are strictly prohibited from learning on-site, visiting, or taking photographs. 3. Responsible for registering visitors. 4. Smoking is strictly prohibited for all visitors, as is bringing any kind of ignition source. 5. During the production shutdown, assist the on-duty staff in conducting on-site inspections, with a particular emphasis on inspections during night shifts. 6. Under the unified leadership of the class monitor, participate in all activities within the class.