Process & Technology for Comprehensive Utilization of Dry Gas in Refinery.
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 the low-carbon hydrocarbon products can effectively reduce the raw material cost of the ethylene plant , improve the economic efficiency of the device.
At this stage, refineries have recovered the dry gas resources of refineries to a certain extent. However, with the expansion of the refining scale, the refinery's dry gas resources have become more and more abundant, and some dry gas resources have not been effectively utilized, 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 and other methods;
For light hydrocarbon resources in dry gas, methods such as cryogenic separation, pressure swing adsorption, oil absorption and separation are usually used to concentrate and recover the light hydrocarbon components.
Process Technology
According to the characteristics of the refinery dry gas, the shallow cooling oil technology combines the ethylene separation technology of the intermediate cooling oil absorption method with the technical characteristics of the FCC absorption stabilization system, and develops a complete set of technology for the recovery of the refinery dry gas by the shallow cooling oil absorption method.
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.
It can efficiently recover ethylene, ethane and other components from various types of refinery dry gas.
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 oil refinery absorption-stabilization system. 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 device operation and maintenance are relatively easy.
The absorption tail gas of the shallow cooling oil technology is concentrated by membrane separation. Considering that the membrane separation technology cannot remove some impurities, the product hydrogen can meet the hydrogen requirements of the pipeline network.
Considering the high recovery rate (96.5%) and relatively low purity (88.3%) of this project, the crude hydrogen can obtain qualified industrial hydrogen through the existing hydrogen production unit PSA.
The parallel PSA technology process is long and relatively complex, and the process uses vacuum pumps, refrigeration units and other rotating equipment and multiple program-controlled valves. According to experience, the operation stability of the device is predicted to be 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/Output Analysis
Using the shallow cooling oil absorption technology, the C2 and ethylene content in the ethylene-rich gas products can meet the requirements of the ethylene plant. Among them, 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.
For the shallow cold oil absorption technology, the C2 recovery rate is >93%. The technology adopts the absorption-desorption process in the tower, and the C2 recovery rate is not affected by the operation period, and the recovery rate can be easily adjusted by increasing or decreasing the circulation amount of the absorbent.
