上海东化环境工程有限公司
Shanghai Donghua Environment Engineering Corp.
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上海东化环境工程有限公司 |
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Shanghai Donghua Environment Engineering Corp. |
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The technology of olefin recovery from refinery offgasBackgroundThe refinery offgas is mainly produced by the second process of raw oil, such as FCC, hydrocracker, delayed coking and so on. The output of offgas produced by FCC is the highest. The main compositions of refinery offgas are H2 , CO, CO2, O2, CH4, C2H4, C2H6, C3H8, C3H6, C＋4. There are also some trace impurities such as S, Hg, As in the gas. The content of ethylene and ethane is about 10～30％, and that of hydrogen is about 20%. Economic ImpactØ Recovery Unit is easily integrated into a Refinery – especially if it is located in proximity to an Ethylene plant. Ø Recovered “Dilute” Ethylene stream can be used as feedstock for EB/Styrene plant or for OCT/Metathesis Ø Hydrogen can be recycled back to the refinery。 Ø Supply comonomer ethylene for fuels-type refinery PP plant Process featuresSDEEC has developed a novel olefin recovery process (NORP) to recover olefin from offgas. It has been improved in two aspects. Firstly, selective hydrogenation catalyst of Süd-Chemie, Inc. is adopted to remove NOx and O2 in the offgas. Secondly, after overhead gas of olefin absorber works in expander cold energy produced can be used to further condense the light olefin in overhead gas, thereby increasing the olefin recovery. The main features of NORP are listed as following. Ø Simple process, and competitive and effective in assembly of equipments. The key equipments are five columns such as acid gas absorber, acid gas stripper, caustic column, light olefin absorber, light olefin stripper, offgas compressor, propylene refrigerator and expander. Except expander, all equipments can be made in homeland and occupation area is small. Ø Few or no peoples required to operate the plant. Most equipments such as columns and heat exchanger belong to static equipments. Compressors and expander are safe and reliable, and their accident rates are very low. The plant is controlled by DCS with high automation. Ø High olefin recovery and great economic income. The ethylene recovery can reach 95% by adopting NORP. The nitrogen content is less than 0.1% in product gas. The recovered product’ quality is good and then it increases very low load to downstream separation unit of ethylene plant. Ø Good adaptability to Feedstock If ethylene content in feed is more than 5%, NORP can be adopted. But for cryogenic separation, only when ethylene content in feed is more than 20%, economic income can come out. Ø Good effect to remove impurities and the product’s quality guaranteed. Adopting selective hydrogenation catalyst of Süd-Chemie, Inc. to remove NOx and O2 of refinery offgas, the NOx content of product is less than 50ppb and then the product can be easily sent to separation unit of ethylene plant. Ø Mature process and reliable equipment The process avoids the cryogenic section. The lowest local temperature is only －70~－85℃, which is higher than the temperature where explosive gums can form. Thus potential hazard in the existence of NOx is eliminated. The advantagesØ Technology is mature and reliable and only the key rotating equipments need be imported. Ø Moderate size and good adaptability Ø Low investment and high income. Ø Safe process and no potential hazard. The olefin recovery process with Refinery/Chem plant next to each otherRefinery offgas enter the compressor firstly, and then enter the acid gas absorber and caustic column to remove CO2/H2S after compression, cooling and gas/liquid separation. After cooling and drying, the offgas is sent to light olefin stripper, and C＋2 compositions are absorbed by oil absorber. The overhead gas of column enters the cold box in order to decrease its temperature and then enter the expander to get work. The cryogenic gas enters the cold box to recover the cold energy and then enter the compressor. One part of gas is used as regenerated gas and the other enter fuel pipeline system. The rich oil in the bottom of light olefin absorber is sent to light olefin stripper. The C2、C3 compositions are separated from oil absorber . The desorption gas is sent to hydrogenation reactor to remove NOx and O2. Pure gas is sent to separation system in ethylene plant to recover ethylene, ethane and propylene and so on.
Option with Refinery/Chem plant next to each other The olefin recovery process with individual refineryRefinery offgas enter the compressor firstly, and then enter the acid gas absorber and caustic column to remove CO2/H2S after compression, cooling and gas/liquid separation. After cooling and drying, the offgas is sent to light olefin stripper, and C＋2 compositions are absorbed by oil absorber. The overhead gas of column enters the cold box in order to decrease its temperature and then enter the expander to get work. The cryogenic gas enters the cold box to recover the cold energy and then enter the compressor. One part of gas is used as regenerated gas and the other enter to fuel pipeline system. The rich oil in the bottom of light olefin absorber is sent to light olefin stripper. The C2, C3 compositions are separated from oil absorber. The desorption gas is sent to hydrogenation reactor to remove NOx and O2 and then is sent to demethanizing column. The compositions from bottom of the demethanizing column enter deethanizing column, and they are be separate C2 composition from top of column and C3 composition from bottom of column. C3 compositions are sent to gas separator unit. C2 compositions are separated to ethylene and ethane in deethanizing column. Ethylene is sent to PP plant as product and ethane is sent to fuel pipeline system.
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