Pyrolysis furnace application furnace tube chemical cleaning technology to improve the thermal efficiency of cracking furnace Zhang Haitao (China Petroleum Daqing Petrochemical Company Chemical No. 1 Plant, Daqing, Heilongjiang, 163714) The use and effect of the furnace were summarized and analyzed.
Therefore, it is necessary to find an effective square piece to solve the high temperature, short residence time and super selective cracking furnace of 8 S Guanguan companies in the old plant of PetroChina Daqing Petrochemical Company Chemical Plant No. 1 (hereinafter referred to as Daqing Ethylene). (EF-111A~G, I). In recent years, due to the poor use effect of the cracking furnace steam soot blower, the convection section coils are ashed and fouled seriously, and the thermal efficiency is greatly reduced.
In April 2005, the chemical reactor developed by a domestic company was used to clean the convection section coil of the cracking furnace, and good results were obtained.
1The reason for chemical cleaning is that the pyrolysis furnace originally designed to crack light hydrocarbons when the temperature is 156 ° C, and the naphtha exhaust temperature is 141 ° C. The actual exhaust gas temperature is 210 ~ 260. The main reason for the exhaust gas temperature of 170-180C in naphtha is that during the operation of the cracking furnace, the tar, sulfide and mineral in the flue gas adhere to the surface of the tube and the fin, plus The flue gas has certain corrosion to the furnace tube. After long-term operation, more and more ash and dirt are accumulated between the surface of the tube and the fin, which causes the heat transfer efficiency of the fin tube to decrease, and the convection section tube group absorbs from the flue gas. The total heat loss, eventually leading to an increase in the temperature of the flue gas, the amount of fuel gas added, the thermal efficiency of the cracking furnace is greatly reduced, and the energy consumption and material consumption of the device are increased. Due to the poor effect of the original steam soot blower, the exhaust gas temperature of the cracking furnace can be reduced by 5~10C after each soot blowing, but the exhaust gas temperature rises again after two days of operation.
The problem of ash and fouling of the convection section coil of the cracking furnace has become an important convection section coil condition of the pre-cleaning cracking furnace which restricts its safety, high efficiency, energy saving and long-cycle operation.
2 chemical cleaning method Because the cracking furnace lining can not contact water, can not be cleaned by traditional immersion or low-input and high-out method to fill the furnace tube with cleaning liquid, only the furnace tube can be sprayed and cleaned. The biggest problem with spray cleaning is that the contact time between the cleaning solution and the dirt is short, and the cleaning dead angle is prone to occur. In particular, when the furnace tubes are arranged in many layers (26 layers) and the dirt is thick, the cleaning effect is difficult to ensure. Therefore, the use of dispersant, stripping agent as the main agent, permeation, wetting agent, corrosion inhibitor as an auxiliary cleaning formula, using special tools and nozzles using the following efficient and quick method of cleaning. It solves the problems of poor cleaning effect, high corrosion rate, lining damage and high cost caused by general cleaning methods.
2.1 Pre-cleaning Pre-cleaning is to spray the penetrant and wetting agent onto the surface of the equipment through automatic metering and special nozzles, so that the pre-cleaning agent gradually wets the surface of the dirt and penetrates into the dirt, thus making the dirt loose and easy. Dissolved.
2.2 Cleaning and cleaning After the equipment is pre-cleaned, the cleaning agent is used to spray the equipment to disperse and emulsify the cleaning agent, so that the dirt is dispersed and dissolved in the cleaning liquid and then flows out.
First, check the protection of the lining in the pre-cleaning, confirm that there is no problem such as the penetration of the cleaning solution, turn on the cleaning pump for cleaning, and meter the cleaning agent. The surface tension, corrosion rate, and pH value of the cleaning solution were measured, and the cleaning nozzle was moved once every 10 minutes, and moved 20 to 30 cm each time to reciprocate. Cleaning time: 2.3 Flushing and rinsing is to spray the stripping agent onto the surface of the equipment through automatic metering and dosing, heating equipment and special nozzles. The stripping agent is used to peel off and clean the residual dirt on the surface of the equipment to further improve the cleaning effect. . The cleaning liquid flow rate is controlled at 30 m3/h, the rinsing time is 4~6 hours, and the pH value is 6~9. After cleaning, the convection section of the cracking furnace is in the condition of 32. The temperature of the exhaust gas is changed after the chemical cleaning of the convection section of the cracking furnace. When the furnace feed amount and COT temperature control are the same as before the cleaning (ie, the same working condition), the exhaust gas temperature is significantly reduced. Table 1 shows the data collected from the convection section exhaust gas temperature before and after chemical cleaning in the middle of the cracking furnace operation. Only the data of four cracking furnaces are listed below (see Table 1).
―111A―D Smoke exhaustion temperature reduction °C Equipment name Before cleaning the exhaust temperature After cleaning, the temperature difference of the exhaust gas is cleaned. After the dirt and impurities on the coil of the convection section of the cracking furnace are cleaned, the medium in the coil and the flue gas in the convection section are obtained. After sufficient heat exchange, the temperature of the raw material after preheating through the coil is obviously higher than that before the cleaning, indicating that the heat exchange effect of the convection section is obviously improved, and the heat transfer efficiency is increased.
Publishin calculates 7 per ton of fuel in a single furnace year i time of 7920e hours. Net 3 use effect 3.1 After cleaning effect ~ On June 30, 8 cracking furnaces in the old area of ​​the ethylene plant were cleaned. After cleaning, the dirt on the surface of the furnace tube, fins and gaps has been basically removed, and the upper part is visible. 4 Economic Benefits The fuel gas consumption of the cracking furnace before and after cleaning under the same working conditions is significantly reduced (see Table 2).
The hourly average fuel gas consumption is 0. 850 yuan, the annual benefit of a single furnace: Table 2 before cleaning. Post-cracking furnace (EF-111A) fuel gas consumption statistics time before cleaning the cracking furnace outlet temperature factory [: feed volume Chuan. h 4 fuel gas consumption eight "114 March 20, March 21, after cleaning, April 26, April 27, 5 Conclusion After the cleaning, the surface of the tube fins has been basically free of dirt, and the convection temperature of the flue gas is significantly reduced. Close to the design index, the fuel gas consumption decreased from an average of 1.912t/h before cleaning to 1.51t/h after cleaning, reducing fuel consumption by 0.402t/h, and reducing fuel consumption by 2.706264 million yuan throughout the year, achieving good cleaning results. Due to proper measures and environmentally-friendly cleaning agents, the cleaning solution has no corrosion to the furnace tube, no harm to the furnace lining, and no pollution to the environment.
But at the same time there are certain problems. For example, because the equipment cleaning is relatively clean, the main equipment is exposed to the air, especially in a humid environment, and it is easy to oxidize and return to rust. However, there is no suitable way to avoid or more mature passivation treatment technology. Of course, the rusting phenomenon will stop after the cracking furnace is turned on. In addition, there are still very few parts in the lower part of the convection section, and the scale forms a thin, dense scale layer. Due to the long-term high temperature state, it is dense and hard, which makes it difficult to remove the complete ethylene online.
Yanshan Petrochemical Refinery's Ethylene Resource Recovery Technology Benefits Recently, Yanshan Petrochemical's “Recycling Refinery Ethylene Resource Complete Industrialization Technology†passed the project appraisal of Sinopec Group Company. Experts believe that the technology is the first in China and the overall technology has reached the international advanced level.
It is reported that the “recycling refinery ethylene resource complete industrialization technology†was jointly developed by Yanshan Petrochemical, Sichuan Tianyi Technology Co., Ltd. and Sinopec Engineering Construction Company, using ethylene and other components in the two-stage pressure swing adsorption concentrated catalytic cracking dry gas. Compared with the cryogenic method and the oil absorption method, this technology has the advantages of low investment, low consumption, and little influence on existing ethylene devices.
Yanshan Petrochemical applied the above technology to build a 30,000 m3/h (standard state) catalytic cracking dry gas enriched ethylene plant, which produced qualified ethylene-rich gas products on August 2, 2005. After the pre-fractionation unit, the ethylene-rich gas was successfully integrated into the corresponding ethylene production unit. The whole system has been running stably for 15 months, which laid a solid foundation for the promotion and application of this technology.
It is understood that the dry gas of the Yanshan Petrochemical Catalytic Cracking Unit has only been used as a fuel to burn off the economic benefits. The above-mentioned 30000Nm3/h catalytic cracking dry gas enriched ethylene device can effectively recover ethylene, ethane, propylene and other resources in the catalytic cracking dry gas, and the economic benefit is remarkable. According to the successful application of this technology, the annual production of chemical light oil for ethylene production is about 120kt, which is 150 million yuan for enterprises. In the next step, the adsorbed exhaust gas can be considered as a raw material for hydrogen production to maximize economic benefits.
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