[ China Environmental Protection Online Product Evaluation ] The hydrogenation reactor is the core equipment of the hydrogenation unit and the key to the hydrogenation process. Do you know how it works, its structure? What are the components and what "role" do they play in the reactor?
The hydrogenation reactor is operated in a high temperature and high pressure hydrogen environment, and the materials entering the reactor often contain impurities such as sulfur and nitrogen, and react with hydrogen to generate corrosive hydrogen sulfide and ammonia. In addition, the hydrogenation reaction is an exothermic reaction, which will increase the bed temperature, but local overheating cannot occur.
Classification of hydrogenation reactor
Depending on the nature of the feedstock oil in the catalytic hydrogenation process, the corresponding process flow and catalyst used
are different, and the reaction forms are different. Generally, there are three types: fixed bed reactor, moving bed reactor Fluidized bed reactor.
According to whether the high temperature medium is in contact with the wall of the reactor under the state of use of the reactor, it can be divided into a cold wall structure and a hot wall structure.
Cold wall reactor
The cold wall reactor is provided with a non-metallic thermal insulation layer on the inner wall of the equipment, and some are also lined with a stainless steel jacket to reduce the design wall temperature of the reactor to below 300 ° C. Therefore, 15CrMoR or carbon steel can be used. There is also no need to surfacing stainless steel, which greatly reduces the difficulty of manufacturing.
However, because the heat insulation layer of the cold wall reactor occupies the inner shell space, the utilization of the reactor volume is reduced, and the material is wasted. Moreover, the non-metal heat insulation layer in the cold wall reactor is under the washout of the medium, or It is easy to be damaged in the change of temperature, it may need to be repaired or replaced after a period of operation, and the cost of construction and repair is high. If the lining comes off during operation, the reactor wall near the place where the lining comes off will exceed the design temperature, and the paint will change color when viewed from the outside. Therefore, the hidden danger of the reactor is greatly increased, and even in severe cases, the device is forced to stop.
Hot wall reactor
The wall of the hot wall reactor is in direct contact with the medium, and the wall temperature is basically the same as the operating temperature, so it is called a hot wall reactor. Although the manufacture of hot-wall reactors is difficult and the one-time investment is high, it can ensure long-term safe operation and is currently widely used internationally.
Internal components of hydrogenation reactor
Due to the exothermic reaction of gas, liquid and solid phases in the hydrogenation process, in order to make the reaction feed (gas and liquid two phases) and the catalyst (solid phase) fully, uniformly and effectively contact, the hydrogenation reactor is designed with Multiple catalyst beds, a distribution tray is set on the top of each bed, and a temperature control structure (cold hydrogen tank) is provided between the two beds to ensure the safe and stable production of the hydrogenation device and extend the catalyst Life.
The reactor is provided with reactor internal components such as an inlet diffuser, a distribution plate, a fouling basket, a catalyst support plate, a catalyst discharge tube, a cold hydrogen tube, a cold hydrogen tank, an outlet collector, and a thermocouple.
The medium from the reactor inlet first passes through the inlet diffuser, and after rectifying in the upper cone, it is diffused across the cross section of the reactor after throttling and collision by the two layers of holes in the upper and lower baffles.
Its main functions are as follows: First, it diffuses the incoming medium to the entire cross section of the reactor. The second is to eliminate the vertical impact of gas and liquid media on the top distribution plate, creating conditions for the stable operation of the distribution plate. The third is to promote gas-liquid two-phase mixing through disturbance.
The top distribution plate consists of a tray plate and distributors evenly distributed on the plate. The top distribution plate is above the catalyst bed, the purpose is to evenly distribute the reaction medium, improve its flow condition, achieve good contact with the catalyst, and then achieve uniform radial and axial distribution. There are many types of distributors. Most of the hydrogenation reactors designed and manufactured by our country use bubble cap type distributors.
In order to better break the liquid entering the downcomer into droplets, and change the liquid flow direction from vertical to oblique downward, causing further diffusion, a crusher can be added under the bubble cap.
On the catalyst bed, the distribution plate is used to uniformly distribute the reaction medium, improve its flow condition, achieve good contact with the catalyst, and then achieve uniform radial and axial distribution.
A basket frame composed of different specifications of stainless steel metal mesh and skeleton is placed on the top of the catalyst bed on the top of the reactor, which can provide a larger flow area for the reaction stream, and trap more mechanical impurities on the top of the upper catalyst bed. Deposits without causing the reactor pressure drop to grow too quickly.
The fouling basket is uniformly arranged in an equilateral triangle on the internal cross section of the reactor, and the inside is empty (without catalyst or porcelain balls). After installation, it must be connected with a stainless steel chain and fastened securely. On the support beam of the upper distribution plate, the stainless steel metal chain must have sufficient length margin (considered by the 5% sink of the bed height) in order to adapt to the sinking of the catalyst bed.
Catalyst support plate
The catalyst support plate consists of a T-shaped beam, a grid and a wire mesh. The two sides of the girders rest on the bosses on the reactor wall, while the grille is placed on the girders and bosses. A layer of coarse stainless steel wire mesh and a layer of fine stainless steel wire mesh are laid on the grid, and magnetic balls and catalysts can be loaded on it.
Catalyst support beams and grids must have sufficient high temperature strength and stiffness. Even under high temperature of 420 ℃, the bending deformation is very small, and it has certain corrosion resistance. Therefore, the materials of the girder, grille and wire mesh are all stainless steel. In the design, the weight of the catalyst and the magnetic ball on the catalyst support plate, the weight of the catalyst support plate itself, the pressure drop on the bed and the weight of the operating fluid should be considered, and the structural dimensions of the support beam and grille should be calculated.
Catalyst discharge pipe
A number of discharge tubes are installed below each catalyst bed of the fixed-bed reactor, across the catalyst support tray, material distribution tray, and cold hydrogen tank, and lead to the next bed to discharge the catalyst when the reactor is stopped. Agent channel.
Cold hydrogen tube
Hydrocarbon hydrogenation is an exothermic reaction. For a multi-bed hydrogenation reactor, the temperature of oil and gas and hydrogen will rise after the reaction in the previous bed. In order to continue the effective reaction in the next bed, it is necessary to Cold hydrogen was introduced between the two beds to control the temperature. The tube that introduces cold hydrogen into the interior of the reactor and spreads it is called a cold hydrogen tube.
The role and requirements of the cold hydrogen addition system are:
Supply a sufficient amount of cold hydrogen evenly and stably.
Cold hydrogen and hot reactants must be thoroughly mixed, and have a uniform temperature and material distribution when entering the next bed.
The cold hydrogen tube is divided into in-line type, dendritic form and ring structure according to the form.
For reactors with smaller diameters, a straight-through structure with simple structure and easy installation is sufficient.
For a reactor with a larger diameter, the mixed effect of the cold hydrogen injected by the in-line cold hydrogen tube and the upper layer is not good, which directly affects the remixing effect of the cold hydrogen tank. At this time, a dendritic or ring structure should be used.
Cold hydrogen tank
The cold hydrogen tank is actually a combination of a mixing tank and a pre-distribution tray. It is a place where the hot reactants and cold hydrogen in the hydrogenation reactor are mixed and heat exchanged. Its role is to fully mix the reaction products flowing from the upper layer with the cold hydrogen injected by the cold hydrogen tube in the box to absorb the heat of reaction, reduce the temperature of the reactants, meet the reaction requirements of the next catalyst bed, and avoid overheating of the reactor .
The layer of the cold hydrogen box is a baffle plate, and the baffle is provided with a throttling hole. The cold hydrogen coming out of the cold hydrogen tube and the oil and gas reacted with the previous bed are pre-mixed on the baffle plate, and then enter the cold hydrogen tank through the orifice. After the cold hydrogen gas entering the cold hydrogen tank and the hot oil and gas coming down from the upper layer are repeatedly deflected and mixed, they flow to the second layer of the cold hydrogen tank-the sieve plate tray, the sieve plate tray, and then baffled on the sieve plate tray again to strengthen the mixing effect. Then make assignments. There is sometimes a bubble cap distribution tray under the sieve plate tray for final distribution of pre-distributed oil and gas.
The exit collector is a hat-shaped part with round holes on the top and long holes on the side walls, covering the stainless steel mesh. Its role is mainly to prevent the porcelain ball at the bottom of the reactor from leaking out of the outlet and discharge the fluid.
The outlet collector at the bottom of the reactor is used to support the lower catalyst bed, reduce the pressure drop in the bed and improve the distribution of reaction materials. There are several gaps on the lower edge of the outlet collector in contact with the lower end head, which is used for draining liquid during shutdown.
In order to monitor the temperature increase of the bed caused by the hydrogen exothermic reaction and the temperature distribution of the bed cross section, the operating temperature was monitored.
Damaged form of hydrogenation reactor
High-temperature hydrogen corrosion
Corrosion of high-temperature hydrogen sulfide
Stress corrosion cracking caused by polysulfuric acid
Tempering brittleness of chromium-molybdenum steel
Hydrogen-induced peeling of austenitic stainless steel surfacing layer
Original title: The principle and structure of the hydrogenation reactor, figure it out at once!