KEPAI (Shanghai) Science & Technology Co Ltd project department Wu Yang and Chinese Dagang Petrochemical Industries Co in the first joint workshop jointly compiled the "Tao snow gas phase cleaning application in decompression device shutdown in paper is included in the" China petroleum and chemical industry "magazine in 2015 eleventh. In this paper, gas cleaning is introduced in detail. Compared with liquid cleaning and passivation, it has the advantages of thorough cleaning, less waste discharge and high cleaning efficiency. The following is the detailed content:

Application of gas cleaning in shutdown of atmospheric and vacuum unit

Tao Wu Yang to play snow

China Petroleum Dagang Petrochemical Industries Co first union workshop 300280

Abstract: the CDU in 2014 first introduced overhaul of gas cleaning technology, this technology is in the refinery shutdown process by blowing steam into the chemical refinery and chemical equipment, the final rapid and efficient removal device of ferrous sulfide, hydrogen sulfide and other substances, to ensure the oil refining and chemical plant nontoxic and harmless explosion point, completely purification. Enter the device in the distillation column stage after the first use of parattah en D742 reagents to remove heavy oil, and then use the parattah en D740 reagent deodorization, passivation, eliminating device in FES and hydrogen sulfide, mercaptan and other harmful substances. As reagents are added directly to the steam, they are evenly distributed with purge steam cleaning equipment. In this paper, the comparison of gas phase cleaning with liquid cleaning and passivation shows that gas phase cleaning has the advantages of thorough cleaning, less waste discharge and high cleaning efficiency. As the technology has just been introduced into China, it is necessary to pay attention to the application method in the field construction. Finally, the suggestions and measures are put forward according to the application of gas cleaning in the atmospheric and vacuum distillation unit.

Summary:It is the first time to use vapour phase chemical cleaning in CDU unit in 2014 TAR.

This technology used in refinery shutdown window.The chemical product was carried to the 

system by steam and eliminate the iron sulfur and hydrogen sulfide to acheive completely 

safety for man in.After deinventorary the Paratene D742 is used when the system start to 

steam out to remove the heavy hydrocarbon. Then use Paratene D740 to eliminate iron sulfide 

and hydrogen sulfide.As the paratene product is carried with steam so it is well distributed 

in system. In this article it mainly compared the advantages of vapour phase chemical cleaning 

with liquid phase chemical cleaning. In the end it list the problem of how to use this 

technology right and suggestions.

　Keywords: gas cleaning, ferrous sulfide and Parra Stern reagent

　　Keywords: vapour phase chemical cleaning， iron sulfide，Paratene product

Preface

The atmospheric and vacuum distillation unit of Dagang Petrochemical Branch Company of PetroChina Co Ltd has a capacity of 5 million tons / year (operation elasticity 60 ~ 120%). During the year shutdown process, the atmospheric and vacuum distillation unit faces the problems of long heat exchange process, many heat exchange equipment, great difficulty in stopping and sweeping, and insufficient steam supply. At the same time, the operators are suffering from heavy physical exertion. In the maintenance stage, existing tower in the container have the probability to the occurrence of spontaneous combustion of ferrous sulfide, the need for removal of ferrous sulfide passivation reaction.

1. Application of device cleaning in calendar year

The CDU in March 2011 for the first time in the park, the heavy oil heat exchange system and vacuum tower lower packing diesel chemical cleaning, chemical cleaning at atmospheric pressure and straight run diesel oil as solvent, replacement of main process, system of closed heating, by adding oil soluble cleaning agent, change the solubility of grease, dissolving in diesel, the labor intensity of operators in the process of blowing device and heat exchange equipment to clean up again to reduce the cost, shorten the time of overhaul, after washing, will waste oil recycling, to recycle, reduce losses. In terms of implementation effect, because the local blind head in the corner position still has not been cleaned up thoroughly in grease, diesel after washing, still need to blow out steam. Compared with the previous shutdown effect, the number of tubes in the heat exchanger is greatly reduced during overhaul.

The previous CDU shutdown are passivation cleaning of the vacuum tower, to prevent the occurrence of vacuum tower of spontaneous combustion of ferrous sulfide in the construction process. The process is in shutdown steam blow after the completion of the vacuum tower of FES, passivation cleaning, removal of ferrous sulfide and other flammable substances. From the top of the pressure tower, the passivation agent is used to establish the middle cycle of the reduction of one, two, and two, respectively, and the recovery of the passivation agent at the bottom of the tower is repeated. But in effect, due to the production process by three fillers and excess vapor some serious corrosion, middle liquid return distribution can not be uniform on the filler layer, no reaction to the local, thus affecting the passivation effect.

2. Application of gas phase cleaning

In 2014, vacuum cleaning technology was introduced for the first time by the atmospheric distillation unit in Shanghai. In the process of using the device, cooling capacity, the main process of basic oil after the retreat, steamed into the tower stage, first using the D742 reagent to remove heavy oil, and then use the D740 reagent of deodorization, passivation, eliminating device in FES and hydrogen sulfide, mercaptan and other harmful substances. As reagents are added directly to the steam, they are evenly distributed with purge steam cleaning equipment.  Compared with liquid cleaning and passivation, the theoretical advantages are obvious.

2.1 cleaning reagent

(1) D742

D742 is a water-soluble surfactant that removes heavy hydrocarbon residues in process equipment. D742 steam through the device into the emulsification, removal of process equipment, metal surface heavy hydrocarbon residues.  Solvents mixed with D742 can effectively remove heavy hydrocarbon residues that are not handled by steam or chemicals alone. D742 contains no inorganic ingredients, and can be completely dissolved in water and degraded by 100 percent.

(2) D740

D740 is a water-soluble surfactant that removes hydrocarbon residues from process equipment. D740 can emulsify hydrocarbons in water, moderate oxidation to remove residual hydrogen sulfide (H2S) and iron sulfide (FeS), and also reduce the explosion limit of various gases and control benzene, toluene, xylene.

2.2 cleaning process

After the device starts to cool down, the system of distillation unit began to shut down and clean diesel oil, the main process lead replacement, closed loop heating cleaning, this process is different from previous chemical cleaning, no additive, closed end cleaning diesel back. The basic retreat of oil after the end of three (flash tower, atmospheric tower and vacuum tower) into the distillation stage, with 6 hours of distillation column will be the mainstream range in need of cleaning device (flash tower system, atmospheric tower and vacuum tower system) to enhance the temperature of 100-130 DEG C; with conditions, into the additive one stage, adding 7, specific as follows:

Fig. -1 schematic diagram of gas phase cleaning process

PIDdrawingofCDU

　　气相清洗覆盖区域和清洗试剂用量如下表：

表-1D742清洗数据 PARATENE  D742  CLEANING  DATA

表-2D740清洗数据 PARATENE  D740  CLEANING  DATA

 　The injection point to the injection of D742 in the first system, the system of emulsified heavy oil, 4 hours after D742 continuous cleaning, after cleaning, replacement of reagents, the use of D740, using the special test paper detection reagent into the cleaning device, cleaning for 12 hours until the end of cleaning.

图-2停工气相清洗时间轴

Vapour phase cleaning timeline

Often the total volume of the pressure relief device cleaning device size: 4621m using D742 reagent fand; 7 barrels of 17.5 barrels; using D740 reagent.

3, gas cleaning effect and analysis

3.1 gas cleaning effect

(1) gas phase cleaning for distillation unit in heavy oil and hydrogen sulfide (H2S), iron sulfide (FeS), light hydrocarbon cleaning, after cleaning device inside the device without oil, hydrogen sulfide and other toxic gases content is 0, the scene observation device of internal heat exchanger, tower partial residual sludge, most you can see the color of the metal wall device equipment. As shown in figure -3 to 6.

图-3减渣（1）-闪底E-1210/3.4

Diagram 3 Reisdue(1)-Flash bottom E-1210/3.4

图-4减渣（1）-闪底E-1210/1.2

Diagram 4 Reisdue(1)-Flash bottom E-1210/1.2

Diagram 5 lightlubeoil E-1206/1.2                                                             Diagram 6 EAS-E1218/1.2

(2) open the equipment manhole at the end of the cleaning, the operator carries the instrument test, and the hydrogen sulfide alarm does not alarm. But the upper part of the tower container has poor cleaning effect. Due to the use of gas phase cleaning, the middle and lower parts can reach each corner of the device by utilizing the better fluidity of the steam. Compared with the liquid phase cleaning, the utility model can be evenly distributed and thoroughly purified.

(3) cleaning passivation, using gas cleaning, no passivation waste water and other pollutants, reducing the sewage treatment load. The water for 10.76t was, and the effluent of wastewater was 236 tons in 2012. The waste water produced by passivation should be treated separately, and the cost of subsequent treatment will be increased.

(4) 2014 shutdown using gas phase cleaning technology takes a total of 85 hours, and in 2012 the use of diesel chemical cleaning and passivation liquid takes a total of 99.3 hours, the use of gas phase cleaning after shutdown last save 14.3 hours, and 7 hours of vacuum evaporating tower tower extension.

(5) due to the cleaning device without downtime, so construction time objective extended gas cleaning, the specific time for each cleaning device: steaming tower and removal before and after removal of the heat exchanger cleaning time for 20 hours, the atmospheric tower and flash end time of purging of the heat exchanger 20 hours, vacuum tower the cleaning time of 21 hours, so if the device can stop, or as much as possible the most devices at the same time the surrender, which can make full use of the gas cleaning time is short, the advantages of high efficiency, shorten the cleaning time of construction.

3.2 cleaning effect analysis

(1) there are problems with filling reagent

The reagent filling pump for Ingersoll Rand diaphragm pump, using the 0.4MPa non purified air as power, the pressure is more than 0.45MPa, not the normal filling reagent. During the steam purging, the steam pressure of the normal inlet device is above 0.7MPa. In order to ensure the normal filling of the reagent, the valve is artificially closed and the feed back pressure is reduced. Due to the large number of heat exchangers in the crude oil flow, the steam speed is reduced after the small steam is delivered to the steam valve, and the purging effect is reduced, especially at the end of the process. There is a localized oil sludge in the heat exchanger, as shown in figure -7:

Diagram 7 Flash tower exchangers E-1213/3.4

　In the tower type container, due to the lack of steam, the effect of the upper tray steam tower is not satisfactory. As shown in figure -8/9.

Diagram 8 vacuum tower cold reflux distributor in first

Diagram 9 vacuum tower cold reflux distributor in first

(2) dealing with experience:

Select a higher pressure diaphragm pump, or use pressure equipment to improve the injection efficiency, so that Parra Stern cleaning reagent fully into the device to achieve cleaning effect.

The manufacturers to provide enough steam, the steam carrying parattah en reagent reach all parts to ensure the quality of cleaning device.

(2) the passivation effect of vacuum tower

Vacuum tower passivation site monitoring, using HydrionpaperQT-10 test paper monitoring water samples, after analysis of the value in 300, as qualified. The first set of monitoring data was started at the time of passivation 8, and the follow-up monitoring intervals were 2h, 1.5h and 1.5h respectively. The statistics are shown in the following table.

Vacuum tower chemical cleaning checking data

From the data analysis, the inspection results are consistent with the span tower, cut the top to a reduction of grease cleaning and passivation effect is not ideal. While the data change trend, also in line with the additive process of normal change, only one vacuum tower additive, reagent with feed into the vacuum tower, the first is from the feed section nearest to the minus three, overflash qualified oil reaction, with the passage of time, minus two, minus the bottom sampling position have qualified. The trend is shown in figure -11.

图-11 减压塔钝化反应趋势变化图 

4. Compare gas phase cleaning with liquid phase cleaning

In 2014, after atmospheric cleaning, the atmospheric vacuum distillation unit has advantages over the previous liquid cleaning, including diesel chemical cleaning and liquid phase passivation, but the gas phase cleaning is more in line with the actual conditions of the device.

Comparison between chemical cleaning and gas cleaning for 4.1 diesel oil

In comparison, in addition to the shutdown shutdown period efficiency, pay more attention to the safety of construction maintenance stage, thus fully guarantee the vapor pressure in the case of not the same time interval of time prolonged steaming tower safety maintenance is a guarantee.

Comparison of 4.2 liquid phase passivation and gas phase cleaning passivation

In addition to the advantages of liquid phase passivation, gas phase passivation has remarkable effects in use, energy saving and emission reduction, and has high shutdown efficiency for the limited shutdown process.

5, concluding remarks

Overall, compared with the previous work of gas cleaning diesel chemical cleaning and passivation liquid has the advantages of saving water, full reaction, but the details still need to be considered comprehensive, in the steam pressure slightly low, distillation effect is not ideal, this can be considered for steam in gas passivation, use steam diffusion to the passive position, play a better effect.