CN102698458B - Method for reducing emission and recycling atmospheric pollutants in emptying and cleaning process of chemical plant installations - Google Patents

Abstract

The invention relates to a method for emission reduction and recovery of atmospheric pollutants in the process of venting and cleaning chemical equipment. Pipelines are erected outside the equipment to be cleaned to form a circulating gas circuit, and the method of steam cycle heating, gasification, integrated split flow and condensation is adopted to improve steam purging transmission. Quality, heat transfer efficiency and reduce the required load of condensing equipment, so as to recover the organic matter remaining after the device returns in liquid form. The invention greatly reduces the requirement on the processing capacity of the condensing system, realizes the emission reduction and recovery of air pollutants in the process of venting and cleaning chemical equipment at a more economical cost, and at the same time solves the problem of direct discharge of some equipment during the purging process because there is no recovery device.

Description

Method for emission reduction and recovery of air pollutants in chemical plant venting and cleaning process

technical field

The invention relates to the fields of clean production and environmental protection, and to clean production, resource recovery, and pollution reduction in industries such as petrochemical, chemical, chemical, pharmaceutical, organic materials, oil products, etc. A method for reducing and recovering air pollutants during the vent cleaning process.

Background technique

All kinds of devices that use organic matter as materials, such as chemical reaction, separation and storage and transportation devices, etc., need to carry out system maintenance and maintenance after a period of operation. The usual steps are parking, material return, cleaning, venting, internal inspection, and device inspection. maintenance etc. After the liquid material is returned, there will inevitably be some residual materials in the device due to adhesion and other reasons. For packed towers or catalytic, heat exchange and other devices, the residual amount of organic materials in the device after the material is returned is considerable. If it is not handled properly, it will cause serious environmental pollution problems. At present, most of the device cleaning uses water washing and steam blowing to clean the residual materials inside the device, providing basic conditions for subsequent device inspection and maintenance. During the cleaning process, part of the material will flow out of the equipment in the form of liquid along with the water flow during the hot water flushing process, while the rest will be discharged from the equipment in the form of gas phase after being vaporized by steam heating and purge. In most cases, this part of the gas phase exhaust gas is directly vented or discharged after being treated by a flare system, and the recovery and purification efficiency of the current flare system are quite limited. Therefore, in the above scenario, the cleaning process of the device loses material resources on the one hand, and causes air pollution emissions on the other hand. At present, there are also some newly-built devices that have condensing devices installed in the purge pipeline to condense the steam purge exhaust and recover some materials. Gas is used for purging. Since there is no macro airflow in most cases inside the equipment, the mass transfer rate is also low, the process takes a long time, and the instantaneous discharge flow during the step-down and exhaust process is large, requiring a large-scale condensing device In order to meet the demand for high-efficiency condensation, the condensing system equipped with the existing production equipment usually cannot meet the required load requirements, and the new large-scale condensing equipment is difficult to implement due to technical and economic problems such as being unusable and idle.

Contents of the invention

The purpose of the present invention is to provide a method for reducing and recovering air pollutants in the venting and cleaning process of chemical equipment in order to overcome the above-mentioned defects in the prior art. Quality, heat transfer efficiency and reduce the required load of condensing equipment. This method can be applied to the recovery of residual organic matter in the venting and cleaning process of equipment in petrochemical, chemical, chemical, pharmaceutical, organic materials, oil storage and transportation industries, and reduce air pollution. gas emissions.

The purpose of the present invention can be achieved through the following technical solutions:

A method for reducing and recovering air pollutants in the process of venting and cleaning chemical equipment. Pipelines are erected outside the equipment to be cleaned to form a circulating gas loop, and steam circulation heating, gasification, and split-flow condensation are used to improve the performance of steam purging, mass transfer, and heat transfer. Efficiency and reduced load on condensing equipment to recover organics remaining after unit return in liquid form.

The method specifically includes the following steps:

(1) Use blind flanges, valves, etc. to isolate all pipes and passages connected to the outside of the device, and isolate all pipes and passages connected to the outside of the device to be cleaned, and then connect the device to be cleaned to the peripheral temporary pipeline and fan power unit Constitute a closed circulation pipeline system;

(2) Connect the condensing system and air flow power system at the upstream and downstream positions of the circulation pipeline system;

(3) Connect the purge steam system with flowmeter and switch to the circulation pipeline system through the steam cleaning pipeline system;

(4) Heat and purge the circulating pipeline system with steam, and carry out steam circulation through the power unit, so as to promote the gasification and evaporation of the residual liquid in the device to be cleaned into the gas phase;

(5) When the vapor pressure in the circulation pipeline system reaches 2-10kg/cm ² or the gas phase concentration in the system no longer rises, turn on the condensation system and the air flow power system for condensation cooling. When the system pressure drops to 0- When the gauge pressure is within the range of 3kg/ ^cm2 , stop the condensing device and the gas flow power device, and recover the organic matter remaining after the device returns in liquid form;

(6) Steps (4), (5) are repeated 2-8 times, and more than 95 wt% of the residual organic matter is discharged from the drain pipe in liquid form.

The circulating air flow rate in the circulating pipeline system is 2 to 50 times the internal volume of the system of the device to be cleaned per hour.

The flow rate of the condensing system is 1 to 10 times the internal volume of the device to be cleaned per hour.

The inlet and outlet of the condensing system can be set at any part of the circulation pipeline system including the spare interface of the device to be cleaned.

The method adopts the periodical operation method of raising the temperature and keeping it warm for a period of time to observe the change of the gas phase concentration, and when the peak value is reached, the temperature is lowered through the condensing system.

The startup and shutdown of the condensing system are interlocked with the temperature or concentration of the circulation pipeline system.

The condensing system adopts one-stage cooling water cooling or two-stage condensation, and the front stage of the two-stage condensation is cooled by cooling water, and the rear stage is cooled by chilled water.

The condensing system is a mobile special equipment or an available condenser in an on-site device system can be borrowed through a pipeline connection.

Compared with the prior art, the present invention is beneficial in that a closed cycle purging pipeline is formed through the construction of a temporary pipeline system, and compared with the open circuit purging system commonly used at present, on the one hand, the pollutants are greatly reduced On the other hand, without increasing the amount of steam, through the turbulent flow transfer process, the transfer rate of heat and substances can be increased, and the time of the distillation tower can be reduced; The condensing equipment realizes the condensation and recovery of the organic matter that has been heated and evaporated into the gas phase during the steam purging process, and realizes the recovery of the residual material after the device returns the material with relatively small equipment investment and operating costs.

Description of drawings

Fig. 1 is a schematic diagram of the recovery process system formed according to the method of the present invention.

In the figure, 1 is the device to be purged and cleaned, 2 is the blind flange of the inlet and outlet pipeline, 3 is the valve of the inlet and outlet pipeline, 4 is the inlet interface of the temporary pipeline of the circulation loop, 5 is the outlet interface of the temporary pipeline of the circulation loop, 6 is the temporary pipeline, 7 is the circulation circuit fan power system, 8 is the pipeline inlet port of the bypass condensing system, 9 is the outlet port of the bypass condensing system pipeline, 10 is the condensing system, 11 is the power fan of the condensing circuit, 12 is the organic matter recovery liquid, and 13 is purging Use the steam system, 14 is the steam purge line inlet, 15 is the temperature sensor of the device itself, 16 is the pressure sensor of the device itself, 17 is the temperature sensor of the temporary pipeline itself, 18 is the pressure sensor of the temporary pipeline itself, 19 is the online VOCs detector, 20 21 is the reboiler of the device, 22 is the top condenser of the device, and 23 is the product tank of the device.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

Steam Purging and Recovery of Petroleum Primary Distillation Tower

1) For an initial distillation tower system (with an inner volume of about 3000m ³ ) in a petroleum refinery, the feed and discharge pipelines are first isolated from the outside air by using valves or blind flanges.

2) Through the inlet port 4 of the temporary pipeline of the circulation loop at the top and bottom of the device and the outlet interface 5 of the temporary pipeline of the circulation loop, the temporary pipeline 6 on the periphery and the power system of the circulation loop fan 7 (rated flow rate 15000m ³ /h) etc. constitute a closed circulation pipeline system.

3) Connect the condensing system 10 and the condensing circuit power fan 11 at the inlet port 8 of the bypass condensing system pipeline and the outlet port 9 of the bypass condensing system upstream and downstream of the closed circulation pipeline system as the air flow power system (rated flow rate ^6000m3 /h).

4) Connect the purge steam system 13 with flow metering and switch to the equipment through the steam purge line inlet 14.

5) Use the device's own temperature sensor 15 and device's own pressure sensor 16 to control the distillation equipment itself, and at the same time install an online VOCs detector 19 in the circulation pipeline.

6) After all the installation of the temporary pipeline is completed, the closed airtight circulation system is fed with 8kg/ ^cm2 gauge pressure steam through the steam purge line inlet 14 and circulated through the circulation loop fan power system 7 at a gas flow rate of ^15000m3 /h. A state of turbulent mass transfer and heat transfer is formed inside the cleaning device 1 to be purged, which promotes the gasification and evaporation of the residual liquid in the cleaning device 1 to enter the gas phase;

7) When the circulation system composed of the cleaning device 1 to be purged and the temporary pipeline 6 reaches the specified steam pressure or temperature (8kg/cm ² gauge pressure), and the online detection data confirms that the gas phase concentration is no longer rising, turn on the condensing system 10 pipe The cooling medium of the road - cooling water and the power fan 11 of the condensing circuit, condensing and cooling with a bypass flow rate of 6000m ³ /h, until the pressure of the device's own temperature sensor 15 drops to the range of 1kg/cm ² gauge pressure, stop condensing the refrigerant supply, stop the condensing circuit power fan 11. So far, the process of steam filling, heating, vaporization and bypass condensation recovery is completed.

8) Repeat steps 6 and 7 to perform 3 new cycle operations, and more than 95% of the original residual oil can be discharged from the condensate drain pipe of the condenser in liquid form, thereby cleaning the equipment on the one hand, and on the other hand in liquid form Recycling materials, thereby reducing emissions to the atmosphere.

Example 2

Steam purge recovery of toluene storage tank

1) For a toluene storage tank system with a volume of ^500m3 , after the material return work is completed, the feed and discharge pipelines are cut off from the outside air by closing the valve or installing a blind flange.

2) Through the inlet port 4 of the temporary pipeline of the circulation loop at the top and bottom of the device and the outlet interface 5 of the temporary pipeline of the circulation loop, the temporary pipeline 6 on the periphery and the power system of the circulation loop fan 7 (rated flow rate 3000m ³ /h) etc. form a closed circulation pipeline system.

3) Connect the condensing system 10 and the condensing circuit power fan 11 at the inlet port 8 of the bypass condensing system pipeline and the outlet port 9 of the bypass condensing system pipeline upstream and downstream of the closed circulation pipeline system as the air flow power system (flow rate 1000m ³ / h).

4) Connect the purge steam system 13 with flow metering and switch to the equipment through the steam purge line inlet 14.

5) The circulation ventilation pipeline is equipped with a temporary pipeline temperature sensor 17 and a temporary pipeline pressure sensor 18 for process control, and an online VOCs detector is equipped upstream of the airflow interface of the condenser inlet of the circulation pipeline.

6) After the installation of all the temporary pipelines is completed, the steam of 2kg/ ^cm2 gauge pressure is introduced into the closed closed circulation system through the inlet 14 of the steam purge line and circulated through the circulation loop fan power system 7 at a gas flow rate of ^3000m3 /h. A turbulent mass transfer and heat transfer state is formed inside the cleaning device 1 to be purged, which promotes gasification and evaporation of the residual liquid in the cleaning device 1 to enter the gas phase.

7) When the circulation system composed of the cleaning device 1 to be purged and the temporary pipeline 6 reaches the specified steam pressure or temperature (2kg/cm ² , gauge pressure), and when the online detection data confirms that the gas phase concentration is no longer rising, start the condensation system 10 The cooling water in the pipeline and the power fan 1 of the condensing circuit are condensed and cooled with a bypass flow rate of 1000m ³ /h until the pressure of the pressure sensor 18 of the temporary pipeline itself drops to the range of 0.02kg/cm ² gauge pressure, and the condensing is stopped Refrigerant supply, stop fan 11. So far, the process of steam filling, heating, vaporization and bypass condensation recovery is completed.

8) Repeat steps 6 and 7 for 2 more cycle operations, and more than 90% of the residual toluene in the original storage tank can be discharged from the condensate drain pipe of the condenser in liquid form, thereby cleaning the equipment on the one hand, and easy to liquid form on the other hand Recycling materials, thereby reducing emissions to the atmosphere.

Example 3

A method for reducing and recovering air pollutants during the venting and cleaning process of a chemical synthesis device. The system structure used is shown in Figure 1. Pipelines are installed outside the device 1 to be cleaned to form a circulating gas circuit, and steam circulation is used to heat and gasify the integrated The method of split condensation improves the efficiency of steam purging mass transfer and heat transfer and reduces the load required by condensation equipment, so as to recover the residual organic matter after the device returns in liquid form.

The method specifically includes the following steps:

(1) Utilize the blind flange 2 of the import and export pipeline and the valve 3 of the import and export pipeline to isolate all the pipes and passages connected to the outside of the device to be cleaned, and then pass through the temporary pipeline inlet interface 4 of the circulation loop and the temporary pipeline outlet interface 5 of the circulation loop. The cleaning device 1 forms a closed circulation pipeline system with the peripheral temporary pipeline 6 and the circulation loop fan power system 7;

(2) Connect the condensing system 10 and the condensing circuit power fan 11 at the inlet port 8 of the bypass condensing system pipeline and the outlet port 9 of the bypass condensing system pipeline at the upstream and downstream positions of the circulation pipeline system;

(3) The steam system 13 for purging with a flowmeter and a switch is connected to the circulation pipeline system through the steam purging line inlet 14;

(4) Heat and purge the circulating pipeline system with steam, and carry out steam circulation through the power unit, so as to promote the gasification and evaporation of the residual liquid in the device to be cleaned into the gas phase;

(5) device self temperature sensor 15, device self pressure sensor 16, device equipment reboiler 21 are installed on device 1 to be cleaned, temporary pipeline self temperature sensor 17, temporary pipeline self pressure sensor 18, temporary pipeline 6 are installed, On-line VOCs detector 19, gas sampling port 20, when the steam pressure in the circulation pipeline system reaches 2～10kg/cm ² or when the gas phase concentration in the system no longer rises, the steam pressure of the circulation pipeline system in this embodiment is 6kg /cm ² , turn on the condensing system 10 and the condensing circuit power fan 11 for condensing and cooling, when the system pressure drops to the range of 0-3kg/cm ² gauge pressure, in this embodiment the system pressure is 1kg/cm ² , stop the condensing device And the gas flow power device, the residual organic recovery liquid 12 after the recovery device returns the material in liquid form, and the product is collected in the device product tank 23 after being condensed by the device tower top condenser 22 arranged on the top of the device 1 to be cleaned;

(6) Repeat steps (4), (5) 2-8 times, adopt heating up and keep warm for a period of time to observe the change of gas phase concentration, when reaching the peak value, pass through the cyclical operation mode of condensing system cooling, the residual organic matter more than 95wt% is liquid The form is discharged from the drain tube.

During operation, the flow rate of the circulating air in the circulation pipeline system is 2 to 50 times the internal volume of the device 1 to be cleaned per hour, 10 times in this embodiment, and the flow rate of the condensing system 10 is 1 to 10 times the volume of the device 1 to be cleaned. The internal volume/hour is 5 times in this embodiment, and the start-up and shutdown of the condensing system 10 are interlocked with the temperature or concentration of the circulation pipeline system. The condensing system 10 adopts one-stage cooling water cooling or two-stage condensing. In this embodiment, two-stage condensing is adopted. The front section is cooled by cooling water, and the rear section is cooled by chilled water. The condensing system 10 used is a mobile special equipment.

Claims (8)

1. A method for reducing and recovering air pollutants in the process of venting and cleaning chemical equipment, characterized in that the method sets up pipelines outside the equipment to be cleaned to form a circulating gas circuit, and adopts steam cycle heating, gasification, integrated split flow and condensation to increase steam Purging the efficiency of mass transfer and heat transfer and reducing the required load of condensing equipment, so as to recover the organic matter remaining after the device returns in liquid form, specifically including the following steps:  (1) Cut off all the pipes and channels connected to the outside of the device to be cleaned, and then form a closed circulation pipeline system with the device to be cleaned, the peripheral temporary pipelines and the fan power unit; (2) Connect the condensing system and air flow power system at the upstream and downstream positions of the circulation pipeline system; (3) Connect the purge steam system with flow meter and switch to the circulation pipeline system through the steam cleaning pipeline system; (4) Heat and purge the circulating pipeline system with steam, and carry out steam circulation through the power device, so as to promote the gasification and evaporation of the residual liquid in the device to be cleaned into the gas phase; (5) When the vapor pressure in the circulation pipeline system reaches 2-10kg/cm ² or the gas phase concentration in the system no longer rises, turn on the condensation system and the air flow power system for condensation cooling. When the system pressure drops to 0- When the gauge pressure is within the range of 3kg/ ^cm2 , stop the condensing device and the gas flow power device, and recover the organic matter remaining after the device returns in liquid form; (6) Repeat steps (4) and (5) 2-8 times to discharge more than 95wt% of the residual organic matter in liquid form from the drain pipe. the 2. The method for emission reduction and recovery of air pollutants in the process of venting and cleaning chemical equipment according to claim 1, characterized in that the flow rate of the circulating air in the circulation pipeline system is 2 to 50 times the internal volume of the device to be cleaned /Hour. the 3. The method for emission reduction and recovery of air pollutants during the venting and cleaning process of chemical equipment according to claim 1, wherein the flow rate of the condensation system is 1 to 10 times the internal volume of the device to be cleaned per hour. the 4. The method for reducing and recovering air pollutants in the process of venting and cleaning chemical equipment according to claim 1, wherein the inlet and outlet of the condensing system can be set in the circulation pipeline system and include the standby interface of the device to be cleaned any part of. the 5. according to claim 1, be used for the method for reducing the emission of air pollutants in chemical plant venting and cleaning process recovery, it is characterized in that, the method adopts heating up and keeping warm for a period of time to observe the change of gas phase concentration, when reaching the peak value, cooling by condensing system Cycle mode of operation. the 6. The method for emission reduction and recovery of air pollutants in the venting and cleaning process of chemical equipment according to claim 1, characterized in that the start-up and shutdown of the condensing system are interlocked with the temperature or concentration of the circulation pipeline system. the 7. The method for emission reduction and recovery of air pollutants in chemical plant venting and cleaning process according to claim 1, characterized in that, said condensation system adopts primary cooling water cooling or two-stage condensation, and said two-stage The front section of condensation is cooled by cooling water, and the rear section is cooled by chilled water. the 8. The method for the emission reduction and recovery of air pollutants in the chemical plant venting and cleaning process according to claim 1, characterized in that, the condensing system is a mobile special equipment or can be used in a field device system through a pipeline connection the condenser. the