| There are many separation and purification methods of refinery gas, such as deep cryogenic separation, membrane separation, pressure swing adsorption separation, the cold oil adsorption separation, metal complex separation, the expander separation, hydrate separation, and some combined process. But the above methods have shortcomes of large investment, high energy consumption, short film life, low adsorption purity, respectively. In our country, refineries are fragmented and small, so just one separation method using is not economical. In this paper, light olefins in dry gas were used to product high value-added LPG production and high octane rating gasoline components, based on the mature technology of light hydrocarbon aromatization.First, industrial experiments of composite and aromatization reaction using dilute ethylene in dry gas were carried out. The best reaction temperature was about 350℃ when regard synthesis gasoline as the main objective product. And by study the main influence of hydrogenation conditions on the product distribution, the general idea was determined that recycle hydrogen after the composite reaction. Stable absorption mathematical model was established according to the material balance and energy balance. RKS equation was selected as the property method, which provided data basis and mathematical basis for the further study on the process. Then using Aspen Plus to simulate the key factors, such as supplement absorption agent, operating pressure of absorption tower and desorption tower, feed position and feed temperature of stabilization tower, etc. The simulation results showed that the the best flow of supplement absorption was 8.5 t/h, the best operating pressure of absorption tower and desorption tower was 1.4MPa and 1.2MPa, respectively. When feed on the 12th boards stage of stabilization tower under the temperature of 135℃, separating effect was better and energy consumption was low. When use activated carbon as adsorbent to recycle hydrogen, under the operating temperature of 35℃ and adsorption pressure of 1.5-2MPa, the purity of obtained hydrogen was 99.99%, hydrogen recovery rate was 95%.Through the process design, on the fixed bed reactor, the conversion rate of olefins in dry gas can reach 97%. The products flow are petrol 0.43 t/h, LPG 0.65 t/h, dry gas 3.29 t/h, hydrogen 0.12 t/h. Estimated according to the current market price, sales can increase more than 3000 millions yuan a year. Considering the economic value of dry gas is low, greater social benefit and economic benefit can obtain if the subject can successfully applied.Given in selectivity of gasoline in the reaction is not high, only about 40%. The key factors affecting gasoline selection is reaction temperature. Considering the ethylene polymerization reaction, hydrogen transfer reaction and isomerization reaction are exothermic process, the cracking and aromatization reaction are endothermic process, the whole process tend to exothermic which may cause local overheating. Macromolecular hydrocarbon cracking speed is faster and product average molecular weight is lower at high temperature. Meanwhile, too high reaction temperature will affect the catalyst life. The advanced CFD numerical simulation was used in this paper, using FLUENT 6.3 to simulate the temperature fields in fixed bed reactor. Many strands of cold feed is used to keep the reactor temperature-remain about 350℃, which can ensure the highest selectivity of gasoline and the longest time of the catalyst. |
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