gTC Lidong

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  • E_CP_0704, edo

  • Aromatics RecoveryRefinery and petrochemical plant process for recovery of benzene, toluene, and mixed xylenes Conventional method: liquid-liquid extraction using sulfolane or glycols Leading-edge technology: extractive distillation using selective solvent blends

    E_CP_0704, edo

  • Comparison of TechnologiesLiquid-liquid extraction: Reliable, wide reference base in industryHigh capital cost, feed flexibility issues, limited potential for improvements Extractive distillation: Modern technology, low-cost, easy to operateSolvents used until recently, have limitations

    E_CP_0704, edo

  • Solvent EffectivenessSolvent NC7/BenzeneTechtiv-100tm2.44Sulfolane2.00N-methyl Pyrolidone1.95N-formyl Morpholine1.89Glycol blends1.35None0.57Solvent power, solvent selectivity, ability to handle wide-boiling feedstock

    Solvent blends offer better performance and high process flexibility

    E_CP_0704, edo

  • EDC/SRC General Flowscheme

    E_CP_0704, edo

  • Design FeaturesSpecialized mass transfer equipment for extractive distillation and solvent recovery columns Heat integrationExtraction block - feed and extract pre-heat, EDC mid-reboiler using lean solvent

    Flexibility in adjusting solvent circulation rates for varying feed quality

    E_CP_0704, edo

  • The working principle of ED is the alteration of the relative volatility of components in the presence of a highly selective solvent. In a mixture containing aromatics and non-aromatics, the relative volatility of the non-aromatic components is enhanced over that of aromatic components in the presence of a solvent.

    Extractive Distillation

    E_CP_0704, edo

  • This enhancement allows the non-aromatics to be distilled overhead in a conventional distillation column, while the aromatics are recovered in the column bottoms. The solvent used in the GT-BTX process is the proprietary blend, Techtiv-100tm, which makes it possible to achieve excellent process performance.

    Extractive Distillation

    E_CP_0704, edo

  • The general flow scheme of the GT- BTXSM process is very simple and consists of two major towers: an extractive distillation column (EDC) and a solvent recovery column (SRC).

    Extractive Distillation

    E_CP_0704, edo

  • Extractive Distillation

    E_CP_0704, edo

  • Hydrocarbon feed is preheated with hot circulating solvent and fed at mid-point into the EDC. Lean solvent is fed at an upper point and selectively extracts the aromatics into the tower bottoms, in a vapor/liquid distillation operation. The non-aromatic hydrocarbons exit the top of the column and pass through a condenser. A portion of the overhead stream is returned to the top of the column as reflux. This washes back any entrained solvent.

    Extractive Distillation

    E_CP_0704, edo

  • Rich solvent from the bottom of the EDC is routed to the SRC, where the aromatics are stripped overhead. Stripping steam is used to facilitate the stripping of the hydrocarbons. The SRC is operated under vacuum to reduce the boiling point at the base of the column. Lean solvent from the bottom of the SRC is passed through a series of heat exchangers, for heat recovery, before returning to the EDC. Extractive Distillation

    E_CP_0704, edo

  • Aromatics overhead product from the SRC is condensed and withdrawn as product. Water from the overhead of the EDC and SRC is collected and vaporized with hot solvent, and used as stripping medium. A solvent regenerator is used to continuously process a small portion of the circulating lean solvent.

    Extractive Distillation

    E_CP_0704, edo

  • The regenerator distills the solvent away from heavy decomposition products, which are purged on a periodic basis from the regenerator bottoms. Since the basic separation in the GT-BTX process is achieved by distillation, the operation of the unit is very simple and intuitive. Control of the main process parameters can be achieved in a manner very similar to that for a regular distillation column.

    Extractive Distillation

    E_CP_0704, edo

  • Basic Operating Scheme

    The aromatic / non-aromatic separation in the Extractive Distillation Column can be divided into the following two steps:1.Aromatic recovery from raffinate (non-aromatics) in the top section of the column2.Stripping the non-aromatic hydrocarbons from the rich solvent in the bottom section of the column

    E_CP_0704, edo

  • Basic Operating Scheme

    Since virtually pure extract is to be produced, the most important performance parameter is the efficient stripping of the non-aromatic from the rich solvent.In the ED process, in the presence of solvent, the heaviest non-aromatics must be more volatile than the lightest aromatics.

    E_CP_0704, edo

  • EDC / SRC Columns

    The differences from liquid extraction are:a.Recovery and purification of aromatic occur in the same columnb.Higher selectivity c.Direct control of the material balance by reboiler duty and draw-off rate. d.Independent control and adjustment of the hydrocarbon and solvent rate

    E_CP_0704, edo

  • Solvent Circulation

    The required solvent rate is based on:Achieving the desired aromatic recovery. More solvent will tend to absorb the aromatic more readily. Sufficient solvent should be used to alter the volatility such that benzene remains less volatile than the raffinate stream

    E_CP_0704, edo

  • Aromatics Recovery FundamentalsMulti-ring aromatics

    Mono-aromatics

    Olefins/ Naphthenes

    ParaffinsC5C6C7C8C9Solvent Selectivity toward Petrochemical HydrocarbonsRelative Effect of Polar Solvents on Hydrocarbon Species

  • Solvent Circulation

    E_CP_0704, edo

  • Solvent Circulation

    Maintaining adequate selectivity between aromatic and non-aromatic at the bottom of the EDC. The solvent displays better selectivity at lower hydrocarbon content at the bottom of EDC relatively compared to solvent content.

    E_CP_0704, edo

  • Solvent Circulation

    E_CP_0704, edo

  • Solvent Circulation

    This means that the higher the aromatic content in the feedstock is, then higher solvent / feed ratio is required to maintain the adequate selectivity.

    E_CP_0704, edo

  • Factors affecting Aromatic recoveryThe factors affecting recovery of aromaticat a given feed rate are:

    Solvent rate and feed compositionED Column feed locationED Solvent temperatureWater Content in solventAromatic content in solventFeed temperatureReflux RatioHydrocarbon content in lean solvent

    E_CP_0704, edo

  • 1.Solvent Rate and Feed Composition Aromatic recovery, feed composition, and solvent/feed ratio (S/F) are closely related.

    E_CP_0704, edo

  • 1.Solvent Rate and Feed Composition In general, as the aromatic content in the feed increases under a given solvent to feed ratio, the relative volatility between the solvent and the raffinate phases will be reduced because more aromatics dissolve in the solvent. This requires a higher solvent to feed ratio to maintain product purity and aromatics recovery

    E_CP_0704, edo

  • 2. ED Column feed location With a fixed number of total stages, the feed point can be adjusted to vary the number of stages above and below the hydrocarbon feed in actual operation in order to meet certain extract purity or aromatic recovery targets.Simply stated, the stages above the feed function to extract aromatic from the hydrocarbon phase and those below the feed to strip the non-aromatic from the rich solvent.

    E_CP_0704, edo

  • 2. ED Column feed location In general, aromatics losses increase when there are fewer stages above the hydrocarbon feed point, while the extract purity will increase by having more stages below the hydrocarbon feed point. More trays below the feed tray are required for high aromatic feed whereas more trays above the feed tray are required for low aromatic feed.

    E_CP_0704, edo

  • 2. ED Column feed location The selectivity ( product purity) is more critical than solvency (product recovery) for high aromatic content in feed, and it is reverse for low aromatic content in feed. As a result, high aromatic feed requires more trays below the feed tray and fewer trays above the feed tray than low aromatic feed.

    E_CP_0704, edo

  • 3. EDC Solvent Temperature The temperature of the solvent entering the EDC is an important factor in controlling the aromatic recovery. The solvent temperature also dictates the column temperature profile because the solvent is the greatest bulk flow rate.

    E_CP_0704, edo

  • 3. EDC Solvent Temperature In general:1.Raising the solvent temperature will improve the recovery of aromatic, through the effect of a higher solvency and reduced viscosity, which improves mass transfer. 2.Raising the temperature slightly lowers the solvent selectivity, which may require a higher heat input (bottoms temperature) to maintain extract quality.

    E_CP_0704, edo

  • 3. EDC Solvent Temperature In general:3. Raising temperature increases the temperature of the raffinate and increases utility requirements slightly.It is important to control the Lean Solventfeed temperature to within +/- 1-2 degC toensure stable operation of the EDC

    E_CP_0704, edo

  • 4. Water Content in Solvent The water content of the solvent is primarily established by the temperature and pressure at the bottom of the solvent recovery column. Typical water content in the solvent is 0.6-0.8wt%. Water decreases the solubility of hydrocarbons in the solvent and therefore decreases aromatic recovery, but directionally improves the extract quali