Process optimization and technology for comprehensive utilization of dry gas resources in refineries
Hydrogen in the dry gas of the refinery is an important chemical raw material for the refinery, and it is mostly obtained from the natural gas hydrogen production process; C2 and C3 in the low-carbon hydrocarbons are used as the raw materials of the ethylene plant, and the recovery of low-carbon hydrocarbon products can effectively reduce the raw material cost of the ethylene plant , improve the economic efficiency of the device.
Refineries have recovered the dry gas resources of the refinery to a certain extent at this stage. However, with the expansion of the refinery scale, the dry gas resources of the refinery have become more abundant. The existing dry gas recovery facilities cannot meet the demand, and some dry gas resources are still not available. Most of them are discharged to the fuel gas pipeline network as fuel, resulting in waste of hydrogen and light hydrocarbon resources.
At present, for hydrogen resources in refinery dry gas, product hydrogen can be obtained by pressure swing adsorption, low temperature condensation, membrane separation, etc.; for light hydrocarbon resources in dry gas, cryogenic separation, pressure swing adsorption, oil absorption and separation are usually used. and other methods to concentrate and recover the light hydrocarbon components.
Technology Overview
The shallow cooling oil technology is a combination of the intermediate cooling oil absorption method for ethylene separation technology and the technical characteristics of the FCC absorption stabilization system, developed by Beijing Chemical Research Institute for the characteristics of the dry gas in the refinery, and the shallow cooling oil absorption method is developed to recover the dry gas in the refinery. Complete set of technologies.
The shallow cooling oil absorption method uses the principle of "similar compatibility", using C4 as the absorbent to absorb the "similar" C2 and above components in the dry gas, while the "dissimilar" H2, N2, O2 , NOx, CO, CH4 and other components are removed, and ethylene, ethane and other components can be efficiently recovered from the dry gas of various refineries.
Process Flow
The combination process of shallow cold oil absorption technology + membrane separation technology is adopted. The shallow cooling oil absorption process is similar to the absorption-stabilization system in the refinery. The raw material is fed into the device and is pressurized by a compressor. The process is simple and conventional equipment is used, and the operation and maintenance of the device are relatively easy.
The absorption tail gas of the shallow cooling oil technology is enriched with hydrogen through membrane separation. Considering that the membrane separation technology cannot remove some impurities, so that the product hydrogen meets the hydrogen requirements of the pipeline network. This project is based on a high recovery rate (96.5%) and a relatively low purity. (88.3%) considered that the crude hydrogen can obtain qualified industrial hydrogen through the existing hydrogen production device PSA.
The parallel PSA technology process is long and relatively complex. The process uses vacuum pumps, refrigeration units and other rotating equipment and multiple program-controlled valves. Based on experience, it is predicted that the operation stability of the device is slightly worse, and the equipment maintenance is relatively complicated.
At the same time, the shallow cooling oil absorbs the exhaust gas with a pressure of 3.2MPa, which can directly enter the membrane separation system; the PSA technology has a lower adsorption exhaust gas, and a compressor needs to be added to the membrane separation part. The process is more complicated, and the investment and energy consumption are greatly increased.
Product Analysis
Using 1# catalytic dry gas, 2# catalytic dry gas and 1# cracked dry gas as raw materials, and adopting shallow cooling oil absorption technology, the C2 and ethylene content indicators in the ethylene-rich gas products produced can meet the requirements of ethylene plants. The content of H2+N2+CO2+CH4 is 4.09%, which is relatively low. If the methane hydrogen content in the ethylene-rich gas is high, it will be unfavorable for the downstream ethylene plant, because the methane hydrogen will occupy more loads of the cracking gas compressor and the cryogenic system, resulting in an increase in the energy consumption of the ethylene plant.
It can be seen that with the increase of the refining scale, the shallow cooling oil absorption technology has great advantages in the treatment of refinery dry gas and the recovery of light hydrocarbon resources.
