vacuum heating furnace working principle
1. Introduction of vacuum heating furnace
Heating furnace is a process in which the action temperature of crude oil is kept at a certain level during processing, storage and transportation without condensation. According to the regulation of heating temperature of pipeline crude oil, the heating temperature of crude oil should not exceed the initial boiling point, and the heating temperature of crude oil rises very little, usually only 40 ~ 50 C. Otherwise, it is easy to change, which will destroy oil production. For the production of oil under heat load, it is necessary to increase the flow of crude oil. Therefore, the heating furnace must rise at a small temperature and work at the flow rate. This requires large capacity for liquid treatment and continuous reheating furnace operation.
2. The working principle of vacuum heating furnace.
The vacuum heating furnace system is mainly composed of the furnace body and other auxiliary equipment. Its working principle is: the hot gas produced by the combustion of hot flue gas is used to radiate heat transfer with fire and smoke pipe, the hot dip fire pipe and smoke pipe medium - water absorbs and produces steam, steam boiling, heat transfer to the heating medium condensation into water, the gravity drop of water. Return to the original place and reheat the steam. Continuous phase change cycles transfer heat to the upper part of the vacuum chamber in the heat exchange medium through "evaporative condensation and evaporative condensation" and heat is heated indirectly; when the process reaches a state of equilibrium, it can be maintained in a furnace with a negative pressure below the local atmospheric pressure stability. With its low cost, low energy consumption, high efficiency, high degree of automation, vacuum heating furnace has become an ideal product, the traditional heating furnace has no great advantage in the oil field.
Vacuum heating furnace has many advantages: safety, mainly because its casing pressure is lower than atmospheric pressure, no explosion, the danger of its operation state is in a closed environment, scaling phenomenon is not obvious; energy saving effect is good; small volume, light weight, easy transfer; the use of automatic control method; adaptability is very wide. The drawbacks of the Vacuum Technology Network (www.chvacuum.com) are that vacuum heaters and auxiliary components, valves and many types of instruments, regardless of which part of the problem, may lead to failure and failure. Vacuum heating furnace will have the following problems: during the operation of the vacuum can not be maintained, furnace water, vacuum valve does not work, vacuum valve leakage, furnace pressure instability.
The heating media in oil and gas gathering and transportation and other fields have obvious differences, which have the following characteristics:
(1) scaling is easy. The formation water is highly mineralized, whether it is heated in oily sewage or water, the scaling tendency is obvious. Because of the high concentration of minerals and the complexity of heating medium, it is very difficult to prevent fouling in reheating furnace.
(2) corrosiveness. The main forms of corrosion to crude oil heating furnace are common: oxygen corrosion, corrosion, pitting corrosion, intergranular corrosion.
(3) high viscosity and low heat transfer coefficient. The crude oil heated indirectly by heating has a high viscosity. Because of its high viscosity, the laminar heat transfer coefficient in the tube is very low, even 1/10 of the water is not available. Therefore, the required heat transfer area is large and the economic influence of the heating furnace is great. Because of the high viscosity of crude oil, the resistance caused by pipe pressure drop also increases.
(4) high pressure. Due to the development of natural gas, heating is achieved by heating furnace before throttling, reaching 40-50 MPa working pressure. Therefore, high quality requirements for the design and manufacture of heat exchangers for reheating furnace.
(5) poor fuel quality. Oil and natural gas heaters use fuels only through rough handling of the fuel, generally water and light hydrocarbon gas, water, sediments and corrosive media of crude oil. If no effective measures are taken, the freezing of natural gas pipelines and control valves may occur in winter, and the moisture concentration in the pressure atomization combustion of crude oil, because the high water content is not easy to ignite and easier to extinguish the problem.
3. Technical characteristics of vacuum heating furnace
3.1, combustion technology
Combustion technology is divided into micro positive pressure ventilation combustion technology and automatic combustion technology. The micro positive pressure ventilation combustion technology refers to the experience of the oil (gas) horizontal internal combustion boiler, adopts the micro positive pressure ventilation combustion mode, thus strengthens the combustion, enhances the cylinder volume heat intensity, causes the combustion excess air coefficient to be controllable in 1.1~1.2, obtains the better technical and economic index; The vacuum heating furnace has the full automatic fuel or the gas combustion. Burner, automatic control can achieve combustion, automatic ignition with a program, high and low level of interlocking protection, extinguishing protection and safety protection functions.
3.2. Heat transfer and heat transfer technology
(1) heat transfer technology for furnace tubes and threaded flue pipes. In order to enhance the heat transfer process and enhance the heat transfer process, the traditional heating furnace tube with straight and smooth fire and smoke is adopted. The heating furnace with corrugated furnace and screw flue tube is adopted to enhance the heat transfer technology. The heating efficiency of the furnace at the same time is reduced and the consumption of steel is reduced.
(2) detachable spiral groove or bellows heating coil. Spiral grooves or bellows are used as heating coils, and the flow tubes in the boundary layer are damaged, and heat transfer is enhanced in the tube. When the coil structure is compact, it is designed as a detachable structure, and forms a detachable connection with the flange and the furnace shell, which makes the maintenance and replacement of the heating coil very convenient.
(3) phase change heat transfer technology. The heat transfer rate of high temperature phase change heat transfer is very high, and small heat transfer can be achieved. The working principle of a vacuum heating furnace using phase change heat transfer technology is that the flue gas heat (radiant heating surface) and the flue gas pipe (convective heating surface) are heated to boiling from the water transferred from the boiler shell to the middle, the water is changed from liquid to vapor evaporation, and the water vapor gradually fills the gas phase space of the furnace, because the coil heating tube wall temperature in the medium is high. The steam is far below the steam temperature, making the steam in the coil. Condensation and heat exchange coil. After condensation water in gravity return water space. Such a cycle of heat transfer process.
(4) In the actual operation of vacuum heating furnace, the intermediate heat transfer medium can be used at high boiling point with lower pressure. Compared with water bath heating and adding latent heat transfer, the heat transfer capability can be improved more effectively, because the heat transfer outside the condensing heat transfer tube can be obtained in the thermal interior of the forced convection heating medium, even in the ordinary carbon steel tube. The best heat exchange effect.
(5) Operate the vacuum heater, because it is vacuum when it is running, then interrupt will open the inlet valve, in the connected atmosphere of the heater, furnace atmosphere, when the heater, and then start, also need to open the inlet valve, the air in the furnace is discharged, the formation of vacuum, but at the same time remove the air will bring out the steam part The result will be a slight drop in the boiler water level, but no drop in the water level will need to be charged, but the boiler water level will be lowered to the allowable minimum, adding water. Practice shows that because of the reliable sealing and normal operation, the small water heating furnace. If clean water is used as an intermediate, non-polluting measure, calcium and magnesium in each water entry is very limited, and can not form a scale in the furnace. In the exhaust process, the air in the furnace is discharged, and the air outside does not have a lot of penetration, so it can be basically regarded as an anaerobic furnace, and can avoid the occurrence of oxygen corrosion, to maximize the service life of the furnace.
(6) Vacuum heating furnaces that pollute the combustion system on the heating surface do not, therefore, reduce the impact of thermal efficiency greatly with the increase of service time. In order to prevent low-temperature corrosion in the tail design of heating, the efficiency is generally 88%-90%. Today, oil and natural gas resources are highly valued, and their prices are increasing. The use of full automatic micro pressure combustion is more complete combustion without causing air pollution.
In summary, vacuum heating furnace has the characteristics of safety, reliability, energy saving and portability, and the advantages of phase change heat transfer technology are obvious. It is suitable for the production and management requirements of oil and gas gathering and transportation in oilfields, and has a wide range of application and popularization value. It is worth further research and development.