Hydrocracking

The basic principle of heavy oil lightening is to change the relative molecular mass and hydrogen-carbon ratio of the oil, and the relative molecular mass and hydrogen-carbon ratio are often changed at the same time. There are two ways to change the hydrogen-carbon ratio of oil, one is decarbonization, and the other is hydrogenation.

Feedstock:Heavy oil, etc.

Products:Light oil (gasoline, kerosene, diesel fuel or feedstock for catalytic cracking and cracking to olefins)

Basic Concepts:

Hydrocracking belongs to the hydrogenation route of petroleum processing, which is to add hydrogen from the outside in the presence of catalyst to improve the hydrogen-carbon ratio of oil products.

Hydrocracking is essentially an organic combination of hydrogenation and catalytic cracking. On the one hand, heavy oil products can be converted into light oil products such as gasoline, kerosene and diesel through the cracking reaction, and on the other hand, it can prevent the catalytic cracking. A large amount of coke is generated, and sulfur, chlorine and oxygen compound impurities in the raw material can be removed by hydrogenation to saturate olefins.

Production process:

According to the state of the catalyst in the reactor, it can be divided into several types such as fixed bed, fluidized bed and suspended bed.

①　Fixed bed hydrocracking

Fixed bed refers to placing the particulate catalyst in the reactor to form a static catalyst bed. The feedstock oil and hydrogen are heated and pressurized to reach the reaction conditions and then enter the reaction system, firstly subjected to hydrorefining to remove sulfur, nitrogen, oxygen impurities and diolefins, and then subjected to hydrocracking reaction. After the reaction product is cooled, separated, depressurized and fractionated, the target product is sent out of the device, and the gas with high hydrogen content (80%, 90%) is separated and used as circulating hydrogen.

The unconverted oil (called tail oil) can be partially recycled, fully recycled or not recycled in one pass.

②　Fluidized bed hydrocracking

The fluidized bed (also known as expanded bed) process drives the movement of a catalyst with a certain particle size by means of the fluid flow rate to form a gas, liquid, and solid three-phase bed, so that the hydrogen, the raw material oil and the catalyst are fully contacted to complete the hydrogenation reaction process. .

The ebullated bed process can process raw materials with high metal content and carbon residue value (such as vacuum residue). And it can deeply convert heavy oil; but the reaction temperature is relatively high, generally in the range of 400~450℃.

This process is relatively complicated and has not been industrialized in China.

③　Suspension bed (slurry bed) hydrogenation process

The suspended bed process is a hydrogenation process that has received renewed attention in order to accommodate very poor quality feedstocks. The principle is similar to that of the ebullated bed. The basic process is that the fine powder catalyst and the raw materials are pre-mixed, and then the hydrogen and hydrogen flow into the reactor from bottom to top. The catalyst is suspended in the liquid phase for hydrocracking reaction. Along with the reaction products, it flows out from the top of the reactor.

The device can process all kinds of heavy crude oil and ordinary crude oil residue, but the investment of the device is large. This process is still in the research and development stage in China.

Production equipment

The main equipment of the hydrogenation process production unit operates under the conditions of high temperature, high pressure and the presence of hydrogen and hydrogen sulfide, so its design, manufacture and material selection are all very demanding, and the control of production operations is also extremely strict.

The high-pressure hydrogenation reactor is the key equipment in the device, with harsh working conditions, difficult to manufacture and high price.

According to whether the medium directly contacts the metal wall, it is divided into two structures: cold wall reactor and hot wall reactor. The reactor consists of two parts: the barrel and the internal structure.

a. Hydrogenation reactor barrel

The reactor barrel is divided into two types: cold wall barrel and hot wall barrel.

b. Hydrogenation reactor internals

The hydrogenation reaction is operated under the conditions of high temperature and high pressure and corrosive media (H2, H2S). In addition to the material to prevent hydrogen corrosion and corrosion of other media, the hydrogenation reactor should also ensure that: reactants (oil and gas and Hydrogen) is evenly distributed in the reactor to ensure good contact between the reactants and the catalyst; the heat of reaction is removed in time to avoid excessive reaction temperature and overheating of the catalyst. In order to ensure the best reaction conditions and prolong the life of the catalyst; under the premise of uniform distribution of reactants, the pressure drop inside the reactor will not be too large, so as to reduce the load of the circulating compressor and save energy.

For this reason, necessary internal components should be set inside the reactor to achieve uniform distribution of gas and liquid as the main goal. Typical reactor internals include: inlet diffusers, gas-liquid distribution trays, descaling baskets, catalyst support trays, quench hydrogen tanks and redistribution trays, outlet collectors, and the like.