Coal tar pretreatment method and system
阅读说明：本技术 一种煤焦油预处理方法及系统 (Coal tar pretreatment method and system ) 是由 程才智 李林 易金华 孙秋荣 章志平 于 2018-09-04 设计创作，主要内容包括：本发明提供了一种煤焦油预处理方法,将过滤后的煤焦油进行脱水、脱石脑油处理后得到低水煤焦油及废液,然后将所述低水煤焦油进行脱酚处理,减少煤焦油中的含酚量得到所述低酚煤焦油,最后往将所述低酚煤焦油与溶剂混合后,注入脱氯剂及破乳剂后,与溶剂进行混合进行电脱盐,脱盐后得到脱盐煤焦油,将所述脱盐煤焦油去除溶剂,最后得到精制煤焦油。本发明的有益效果在于经本方法处理过的煤焦油其有机氯含量大大降低,所排出的废水含酚量较少,解决了煤焦油预处理过程中易结焦,脱盐过程中易乳化的问题。(The invention provides a coal tar pretreatment method, which comprises the steps of dehydrating filtered coal tar, removing naphtha to obtain low-water coal tar and waste liquid, dephenolizing the low-water coal tar to reduce the phenol content in the coal tar to obtain the low-phenol coal tar, mixing the low-phenol coal tar with a solvent, injecting a dechlorinating agent and a demulsifier, mixing with the solvent to perform electric desalting, desalting to obtain desalted coal tar, removing the solvent from the desalted coal tar, and finally obtaining refined coal tar. The method has the advantages that the organic chlorine content of the coal tar treated by the method is greatly reduced, the phenol content of the discharged wastewater is low, and the problems of easy coking in the coal tar pretreatment process and easy emulsification in the desalting process are solved.)
1. A coal tar pretreatment method is characterized in that filtered coal tar is dehydrated and subjected to naphtha removal treatment to obtain low-water coal tar and waste liquid, then the low-water coal tar is subjected to dephenolization treatment to reduce the phenol content in the coal tar to obtain low-phenol coal tar, finally the low-phenol coal tar is mixed with a solvent, then a dechlorinating agent and a demulsifier are injected into the mixture, the mixture is mixed with the solvent to perform electric desalting, desalted coal tar is obtained after desalting, the solvent is removed from the desalted coal tar, and finally refined coal tar is obtained.
2. The coal tar pretreatment method according to claim 1, characterized in that the coal tar is dehydrated by vacuum stripping, wherein the temperature of the coal tar is 140-150 ℃ and the vacuum degree is 300-450 mmHg during dehydration; the stripping gas is an inert gas or low pressure superheated steam.
3. The coal tar pretreatment method according to claim 1, characterized in that the low-water coal tar is dephenolized under vacuum at a temperature of 300 ℃ to 350 ℃ and a vacuum degree of 300mmHg to 450 mmHg.
4. The coal tar pretreatment method according to claim 1, characterized in that the low-phenol coal tar is mixed with a naphtha solvent of C5-C12 in a weight ratio of 1: (0.25-0.5), adding 10-30 ppm of demulsifier and 10-60 ppm of dechlorinating agent, and controlling the temperature of the electric desalting at 140-160 ℃.
5. The coal tar pretreatment method according to claim 1, wherein the desalted coal tar is subjected to solvent removal at 270 ℃ to 330 ℃.
6. The coal tar pretreatment method according to claim 1, further comprising the steps of separating the waste liquid to obtain phenol-containing wastewater, naphtha and part of dissolved oxygen; and (3) after the desalted coal tar is subjected to solvent removal treatment, recovering the removed solvent and mixing with the low-phenol coal tar.
7. The system for realizing the coal tar pretreatment of claim 1, which is characterized in that the coal tar pretreatment system is formed by sequentially connecting a dehydration tower, a dephenolization tower, a mixer, an electric desalting device and a solvent separation tower; the mixer is connected with the tower bottom of the dephenolizing tower.
8. The coal tar pretreatment system according to claim 7, wherein the pretreatment system further comprises a reflux drum, a first heating furnace, a second heating furnace and a solvent heat exchanger; the reflux tank is connected with the top of the dehydrating tower, the first heating furnace is connected with the bottom of the dehydrating tower and the dephenolizing tower, the second heating furnace is connected with the electric desalting device and the middle part of the solvent separation tower, and the solvent heat exchanger is connected with the top of the solvent separation tower and the heat exchanger.
9. The coal tar pretreatment system according to claim 8, wherein a phenol oil outlet is arranged at the top of the dephenolizing tower, and the reflux tank comprises a naphtha outlet and a phenol-containing wastewater outlet.
Technical Field
The invention belongs to the field of coal tar processing, and particularly relates to a coal tar pretreatment method and a coal tar pretreatment system.
Background
With the decrease of crude oil resources, the exploration and the expansion of raw material sources in the petroleum processing industry become an urgent matter at present, coal tar (coal tar: liquid products obtained in the processes of dry distillation, pyrolysis and gasification of coal) is regarded as a hazardous waste, and the recycling value of the coal tar is gradually valued. In all types of coal tar, impurities are contained which are harmful or have adverse effects on production equipment, particularly hydrogenation production equipment, hydrogenation catalysts and product quality. The impurities are mainly water (1.5-4.5%), metal (100-400 mug/g), solid impurities (2-5%) and oxygen-containing compounds (10-30%). The water in the coal tar can cause the operating temperature fluctuation of the heating furnace, so that the fuel consumption is increased, the equipment pressure change is caused after the water is vaporized, and the catalyst is aged by the water vapor, so that the activity is reduced or the catalyst is pulverized to block the hydrogenation reactor. The metals contained in the coal tar are mainly sodium, magnesium, calcium, iron and the like, and the metals not only cause damage to hydrogenation production equipment and pipelines, but also poison and inactivate hydrogenation catalysts particularly seriously. The solid impurities in the coal tar mainly comprise fine coal powder, coke powder, carbon black and the like, and the solid can cause serious blockage to hydrogenation production equipment and pipelines, particularly to hydrogenation reactor beds.
The medium-low temperature coal tar contains more oxygen-containing compounds and chain hydrocarbons, wherein the content of phenol and derivatives thereof reaches 10-30%, the content of alkane hydrocarbons is about 20%, and the content of heavy oil (tar pitch) is relatively low. The chemical equilibrium constant value of the oxygen-containing compound hydrodeoxygenation reaction is large, the reaction equilibrium is favorable, the hydrodeoxygenation reaction is a strong exothermic reaction, and the temperature runaway of a reactor is easily caused in the hydrogenation reaction process. The coal tar contains low-carbon olefin and diene, the diene is easy to coke, and the coal tar has a coking tendency at about 200 ℃; the coke powder and coal powder contained in the coal tar are used as the coke nucleus of the coal tar diolefin raw coke, so that a coking substance is more easily generated.
Phenol is an oxygen-containing derivative of an aromatic hydrocarbon, the hydroxyl group of which is directly attached to the benzene ring. Phenolic compounds are listed as one of a black list of 129 priority control pollutants by the U.S. national environmental protection agency, and are listed as one of the major solutions of harmful wastewater in the water pollution control of China.
The phenol-containing waste water can be inhaled through the contact of skin and mucous membrane or invade into the organism through oral cavity, and after contacting with protein in cytoplasm, insoluble protein is formed to inactivate cells, especially has great affinity to nervous system, and is pathological change of nervous system. Phenol-containing wastewater also has a serious impact on water supply sources and aquatic organisms. When the content of phenolic substances in the water is 0.002mg/L, phenol odor is generated in the process of adding chlorine into the water body; water with concentration more than 0.005mg/L can not be drunk; the concentration is more than 0.1mg/L, and the fish meat in the water has a phenolic taste and cannot be eaten; when the concentration is more than 1mg/L, the serious influence is caused on the activities of reproduction and the like of the fish; and when the content of phenols in the water is more than 10mg/L, aquatic organisms such as fish and the like cannot survive. In addition, the phenol-containing waste water also has an influence on crops. The low-concentration phenol-containing wastewater irrigates farmlands, so that some crops contain phenolic substances and cannot be eaten; the high concentration of phenol-containing wastewater can cause crop death when used to irrigate farmland.
Therefore, in the coal tar hydrogenation process, the coal tar needs to be subjected to purification pretreatment: the solid removal, dehydration, desalination and the like, and simultaneously, the treatment cost of the phenol-containing wastewater is higher due to the complex phenol-containing wastewater treatment process, so that the discharge of the phenol-containing wastewater is reduced as much as possible.
In patent ZL200610105277.6, a tar electric field purification technology is disclosed, the method comprises the following steps of ① preparing mixed oil, mixing coal tar and diluent oil (diesel oil or hydrogenation generated oil) according to a mass ratio of 1 (0-0.25) by using a mixing pump, adding a demulsifier and the like, heating to 130-150 ℃, ② mixing the tar and purified water after primary electric dehydration and heating, then dewatering in an electric field, mixing ③ secondary electric dehydration tar and purified water, then dewatering in the electric field, mixing ④ tertiary electric dehydration tar and purified water, then dewatering in the electric field, and discharging impurity-containing sewage discharged from the coal tar by ⑤ sewage by primary electric dehydration.
In patent ZL01269170.4, an electric dehydration device for coal tar is disclosed. The dewatering device is provided with a dewatering tank, wherein an electrified electrode plate is arranged below a horizontal central line in the dewatering tank and is connected with a high-voltage lead-in rod, and the high-voltage lead-in rod is connected with a dewatering transformer through a high-voltage flexible cable. Because the traditional alternating current electric field technology is adopted in the patent, the traditional processes and equipment have the characteristics of complex process, high energy consumption and the like. Therefore, patent ZL200720182609.0 proposes a skid-mounted AC/DC composite electric field coal tar desalting and dewatering device.
The coal tar pretreatment method has the following problems in practice that ① does not solve the problem of easy coking in coal tar processing, ② has large discharge amount of phenol and salt-containing sewage, ③ has poor diluent dissolving effect, a desalting system is easy to form emulsion, and the operation is unstable.
Disclosure of Invention
In order to solve the technical defects, the invention provides a coal tar pretreatment method and a coal tar pretreatment system.
The specific technical scheme is as follows:
a coal tar pretreatment method is characterized in that filtered coal tar is dehydrated and subjected to naphtha removal treatment to obtain low-water coal tar and waste liquid, then the low-water coal tar is subjected to dephenolization treatment to reduce the phenol content in the coal tar to obtain the low-phenol coal tar, finally the low-phenol coal tar is mixed with a solvent, then a dechlorinating agent and a demulsifier are injected into the mixture, the mixture is mixed with the solvent to perform electric desalting, desalted coal tar is obtained after desalting, the solvent is removed from the desalted coal tar, and finally refined coal tar is obtained.
In the technical scheme, the coal tar is dehydrated in a vacuum stripping mode, the temperature of the coal tar is 140-150 ℃ during dehydration, and the vacuum degree is 300-450 mmHg; the stripping gas is an inert gas or low pressure superheated steam.
In the technical scheme, the low-water coal tar is dephenolized under the vacuum condition, the dephenolizing temperature is 300-350 ℃, and the vacuum degree is 300 mmHg-450 mmHg.
In the technical scheme, the low-phenol coal tar and a naphtha solvent of C5-C12 are mixed according to the weight ratio of 1: (0.25-0.5), adding 10-30 ppm of demulsifier and 10-60 ppm of dechlorinating agent, and controlling the temperature of the electric desalting at 140-160 ℃.
In the technical scheme, the desalted coal tar is subjected to solution removal at 270-330 ℃.
In the technical scheme, the coal tar pretreatment method further comprises the following steps of separating the waste liquid to obtain phenol-containing waste water, naphtha and part of dissolved oxygen; and (3) after the desalted coal tar is subjected to solvent removal treatment, recovering the removed solvent and mixing with the low-phenol coal tar.
The system for realizing the coal tar pretreatment is characterized in that the coal tar pretreatment system is formed by sequentially connecting a dehydration tower, a dephenolization tower, a mixer, an electric desalting tower and a solvent separation tower; the mixer is connected with the tower bottom of the dephenolizing tower.
In the above technical scheme, the pretreatment system further comprises a reflux tank, a first heating furnace, a second heating furnace and a solvent heat exchanger; the reflux tank is connected with the top of the dehydrating tower, the first heating furnace is connected with the bottom of the dehydrating tower and the dephenolizing tower, the second heating furnace is connected with the electric desalting device and the middle part of the solvent separation tower, and the solvent heat exchanger is connected with the top of the solvent separation tower and the mixer.
In the technical scheme, the top of the dephenolizing tower is provided with a phenol oil outlet, and the reflux tank comprises a naphtha outlet and a phenol-containing wastewater outlet.
Compared with the prior art, the method has the beneficial effects that the organic chlorine content of the coal tar treated by the method is greatly reduced, the phenol content of the discharged wastewater is less, and the problems of easy coking in the coal tar pretreatment process and easy emulsification in the desalting process are solved.
Drawings
FIG. 1 is a diagram of a coal tar pretreatment system;
the method comprises the following steps of 1-a dehydrating tower, 2-a dephenolizing tower, 3-a mixer, 4-an electric desalting device, 5-a solvent separation tower, 6-a reflux tank, 7-a first heating furnace, 8-a second heating furnace, 201-a phenol oil outlet, 601-a naphtha outlet and 602-a phenol-containing wastewater outlet.
Detailed Description
The present invention will be described in detail with reference to the following drawings and embodiments.
A coal tar pretreatment method is characterized in that filtered coal tar is dehydrated and subjected to naphtha removal treatment to obtain low-water coal tar and waste liquid, then the low-water coal tar is subjected to dephenolization treatment to reduce the phenol content in the coal tar to obtain the low-phenol coal tar, finally the low-phenol coal tar is mixed with a solvent, then a dechlorinating agent and a demulsifier are injected into the mixture, the mixture is mixed with the solvent to perform electric desalting, desalted coal tar is obtained after desalting, the solvent is removed from the desalted coal tar, and finally refined coal tar is obtained.
In the technical scheme, the coal tar is dehydrated in a vacuum stripping mode, the temperature of the coal tar is 140-150 ℃ during dehydration, and the vacuum degree is 300-450 mmHg; in the traditional process, direct desalination is adopted, water is required to be injected to dissolve salt in tar in the desalination process, and the tar contains more phenol, so that the phenol-containing wastewater in the traditional process is large in amount. The invention firstly dehydrates, because the low-carbon olefin and the alkadiene in the raw materials have lower boiling points and can be removed together with water in the dehydration process, and the low-carbon olefin and the alkadiene are precursors of tar coking, the dehydration firstly greatly reduces the content of the water containing phenol and the risk of tar coking.
The stripping gas is inert gas or low-pressure superheated steam; the inert gas is nitrogen or fuel gas, the low-pressure superheated steam is in the range of 0.3MPa to 1.0MPa, and the superheated temperature of the superheated low-pressure steam is 400 ℃; superheated steam is required to be reduced as much as possible, and phenol-containing sewage is prevented from being generated after the steam and the phenol oil on the tower top are condensed together.
In the technical scheme, the low-water coal tar is dephenolized under the vacuum condition, the dephenolizing temperature is 300-350 ℃, and the vacuum degree is 300 mmHg-450 mmHg.
In the technical scheme, the low-phenol coal tar and C5~C12The naphtha solvent is mixed according to the weight ratio of 1: (0.25-0.5), controlling the specific mixing proportion according to the mixed oil density of less than 0.98, adding 10-30 ppm of demulsifier and 10-60 ppm of dechlorinating agent, and controlling the temperature of electric desalting at 140-160 ℃; coal tar contains more polycyclic aromatic hydrocarbon and C5~C12The naphtha solvent should increase its aromatics content, where C6～C7The narrow fraction is most pronounced, C6～C7The narrow fraction has improved solubility in coal tar compared with diesel fractionThe solubility, the solvent ratio and the emulsion formation are reduced, and the operation is stable and reliable. The dechlorinating agent is not injected, the organic chloride removal rate of the electric desalting is less than 1 percent, and the organic chloride removal rate of the coal tar can reach 60 percent after the TLV-1 dechlorinating agent is adopted.
In the technical scheme, the desalted coal tar is subjected to solution removal at 270-330 ℃.
In the technical scheme, the coal tar pretreatment method further comprises the following steps of separating the waste liquid to obtain phenol-containing waste water, naphtha and part of dissolved oxygen; and (3) after the desalted coal tar is subjected to solvent removal treatment, recovering the removed solvent and mixing with the low-phenol coal tar.
The system for realizing the coal tar pretreatment is characterized in that the coal tar pretreatment system is formed by sequentially connecting a
In the above technical scheme, the pretreatment system further comprises a reflux tank 6, a
The top of the dephenolizing
The water content of coal tar is 2-4%, and the water injection amount of electric desalting is 8-10%; dephenolizing measures are set before coal tar enters electric desalting, so that the content of phenol dissolved in water in the electric desalting water injection process is reduced, and the discharge amount of phenol-containing wastewater is 2-4%; the discharge amount of the waste water containing phenol and salt by adopting the phenol-free process is 10 to 14 percent; the invention greatly reduces the discharge of the phenol-containing wastewater.