gTC Lidong Training.ppt

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.


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).


E_CP_0704, edo


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.


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.


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.


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 quality from EDC.

E_CP_0704, edo

4. Water Content in Solvent A small amount of water can be added to the base of the EDC, if necessary to keep the EDC bottom temperature lower than 175oC, to increase the aromatic purity.Benzene recovery versus water content in lean solvent is shown in graph no. 18.

E_CP_0704, edo

4. Water Content in Solvent

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5. Aromatic content in Solvent Aromatics that are not completely stripped in the SRC and remain in the solvent lead to greater aromatic losses in the EDC than would be experienced with an aromatic-free solvent. The aromatic content of the solvent is depending by the temperature in the base of the solvent recovery column and by the quality of the stripping steam.

E_CP_0704, edo

5. Aromatic content in Solvent At higher aromatic content or higher molecular weight extract, more stripping steam or a higher bottom temperature will be required to maintain the aromatic below a few tenths of a percent in the solvent.

E_CP_0704, edo

6. Feed Temperature Benzene recovery doesnt change rapidly with a change in feed temperature.

E_CP_0704, edo

6. Feed Temperature

E_CP_0704, edo

Chart4

99.996799.92299.76

10099.92299.76

10099.9299.76

10099.9299.76

10099.9299.76

10099.919499.76

10099.91799.76

99.9799.89599.735

97.09697.9599.213

EDC BTM Temperature = Constant; S/F Ratio = 2.2 @ 105 C

Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Feed Temperature, oC

Benzene Recovery, wt%

Benzene Recovery vs. Feed Temperature

input

Feed Temp.67.0077.0087.0097.00107.00117127137147

Bz Recovery, wt%99.9299.9299.9299.9299.9299.919499.91799.89597.95

Toluene Recovery, wt%100.00100.00100.00100.00100.00100.00100.00100.00100.00

Overall Recovery, wt%99.9999.9999.9999.9999.9999.98699.98599.9899.6559

Impurity in BTM, wppm263446628712718686613885

Energy, MMKcal/hr26.0525.3724.6823.9723.2522.507621.753917.518410.1467

Solvent Loss,wppm0.490.490.490.490.490.490.490.490.48

EDC BTM Temperature,C177177177177177177177177177

S/F Ratio(Volume basis)2.202.202.202.202.202.202.202.202.20

Solvent Temperature(C)105105105105105105105105105

Reflux (R/(R+D))0.250.250.250.250.250.250.250.250.25

Feed Temp.67.0077.0087.0097.00107.00117127137147

Bz Recovery, wt%100.00100.00100.00100.00100.0010010099.9797.10




Energy, MMKcal/hr25.1624.4823.7823.0722.3421.6120.8616.629.3





Reflux (R/(R+D))0.150.150.150.150.150.150.150.150.15

Feed Temp.67.0077.0087.0097.00107.00117127137147

Bz Recovery, wt%99.7699.7699.7699.7699.7699.7699.7699.73599.213




Energy, MMKcal/hr27.2326.5525.8525.1424.4223.6822.9318.6911.28





Reflux (R/(R+D))0.350.350.350.350.350.350.350.350.35

recovery

recovery

99.996799.92299.76

10099.92299.76

10099.9299.76

10099.9299.76

10099.9299.76

10099.919499.76

10099.91799.76

99.9799.89599.735

97.09697.9599.213

EDC BTM Temperature = 177 CS/F Ratio = 2.20 @ 105 C

Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Feed Temperature, C

Bz Recovery, wt%

Feed Enthalpy

loss

loss

4.30.490.12

4.30.490.12

4.30.490.12

4.30.490.12

4.30.490.12

4.30.490.12

4.30.490.12

4.30.490.12

4.720.480.12


Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Feed Temperature, C

Solvent Loss, wppm

Feed Enthalpy

energy

energy

25.156726.0527.225

24.47825.3726.5453

23.7824.67825.851

23.0723.968825.14

22.3423.246224.42

21.6122.507623.68

20.8621.753922.93

16.6217.518418.69

9.310.146711.28


Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Feed Temperature, C

Reboiler Duty, MMKcal/Hr

Feed Enthalpy

impurity

impurity

3712611

4173415

4664619

5246226

6068736

72212751

85618674

1790866488

18928138854804


Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Feed Temperature, C

Impurity, wppm

Feed Enthalpy

7. Reflux RatioThe effect of reflux ratio on benzene recovery at various solvent temperature shown in graph no. 12.

At solvent design temperature, the higher reflux ratio decreases the benzene recovery.

E_CP_0704, edo

7. Reflux Ratio

E_CP_0704, edo

Chart2

98.999.999520.15

98.7999.97110.2

98.799.920.25

98.6699.8480.3

98.6599.75140.35

98.6499.6799.9844

98.6499.633199.939

EDC BTM = Const; S/F Ratio = Const

Design

Solvent Temp 95 C

Solvent Temp 105C

Solvent Temp 110C

Reflux, R/(R+D)

Bz. Recovery, wt%

Benzene Recovery vs. Reflux Ratio

Sheet1

Reflux (R/(R+D))0.150.200.250.300.350.400.450.500.550.600.65

Reflux on Feed( Vol%)8.3011.7615.7020.1425.4431.4838.5546.8256.90

Bz Recovery, wt%100.0099.9799.9299.8599.7599.6799.6399.75100.00



Impurity in BTM, wppm573146885836221381,561

Energy, MMKcal/hr22.3622.7723.2523.7824.4525.1826.0327.0028.20





Reflux (R/(R+D))0.150.200.250.300.350.400.450.500.550.600.65

Bz Recovery, wt%99.9099.8399.7299.5899.4399.2999.1999.3099.8199.99

Toluene Recovery, wt%100.00100.00100.00100.00100.00100.00100.00100.00100.00100.00


Impurity in BTM, wppm1821238254342213745933.00

Energy, MMKcal/hr22.3822.7823.2723.7624.4525.1425.9727.0228.2929.761

Solvent Loss,wppm4.301.320.500.240.120.070.040.030.020.0140

Reflux (R/(R+D))0.150.200.250.300.350.400.450.500.550.600.65


Bz Recovery, wt%98.9098.7998.7098.6698.6598.6498.6499.88




Energy, MMKcal/hr24.6224.7325.2125.7626.3727.1227.9828.9530.13





Reflux (R/(R+D))0.150.200.250.300.350.400.450.500.550.600.65

Reflux on Feed( Vol%)11.6815.6120.1025.3231.0038.6746.8056.9469.4684.90

Bz Recovery, wt%99.9899.9499.92100.00


Overall Recovery, wt%100.00100.00100.00100.00100.0099.9999.99100.00100.00100.00

Impurity in BTM, wppm6,0404,4923,0591,6474524147056,15215,913

Energy, MMKcal/hr21.7922.2722.8123.4424.2325.0826.0127.2228.7530.60

Solvent Loss,wppm6.501.750.660.310.160.090.050.030.020.020.01


S/F Ratio(Volume basis)2.202.202.202.202.202.202.202.202.202.202.20


impurity

impurity

37.75730

28.4145.936040

20.94588.0614492

14.8858.1053059

10.535.71647

7.0721.966245

4.6313.2724

37.7950814

6329.71561704.6

EDC BTM Temp.= ConstS/F Ratio = Const.

Design

Solvent Temp. 95 C

Solvent Temp. 105 C

Solvent Temp. 110 C

Reflux (R/(R+D))

Impurity in bottom, wppm

Impurity vs Reflux ratio at const. solvent temp.

recovery

recovery

98.999.999520.15

98.7999.97110.2

98.799.920.25

98.6699.8480.3

98.6599.75140.35

98.6499.6799.9844

98.6499.633199.939

EDC BTM = ConstS/F Ratio = Const

Design

Solvent Temp 95 C

Solvent Temp 105C

Solvent Temp 110C

Reflux, R/(R+D)

Bz. Recovery, wt%

Bz Recovery vs Reflux ratio at const solvent temperature

loss

24.619822.35760.15

24.732422.769921.7929

25.2123.254422.2684

25.755623.778822.806

26.372224.45123.439

27.121425.18424.2267

27.981826.027725.0817

28.952226.997326.014

Design


Solvent Temp. 95 C

Solvent Temp 105C

Solvent Temp. 110C

Reflux, R/(R+D)

EDC Reboiler Duty, MMKcla/Hr

EDC Reboiler Duty vs reflux ratio at const solvent temperature

1.964.091836.5

0.651.237881.75

0.270.482540.659

0.130.234420.3066

0.07460.1180.157

0.0440.06760.085

0.028690.04130.0509

0.02090.0270270.0327

0.0160.01870.02

000.015

0.650.650.0118

EDC BTM Temp = ConstS/F Ratio = Const

Design

Solvent Temp. 95 C

Solvent Temp. 105 C

Solvent Temp. 110 C

Reflux( R/(R+D))

Solvent Loss, wppm

Solvent Loss vs Reflux Ratio

8. Hydrocarbon content in Lean SolventExcessively high hydrocarbon in lean solvent will affect aromatics recovery more than product purity. If the lean solvent includes too high a hydrocarbon, the hydrocarbon can be lost to the raffinate at the EDC as a aromatics reentry loss to raffinate from the lean solvent. In this case, concentration of other aromatics heavier than benzene can be higher than that of benzene in the raffinate product.

E_CP_0704, edo

8. Hydrocarbon content in Lean SolventA typical hydrocarbon content in lean solvent is less than 1.0 wt%. However, Hydrocarbon in lean solvent has little effect on product recovery and purity even if the hydrocarbon content in the lean solvent is as high as 5 wt%.The hydrocarbon content in lean solvent is controlled by stripping steam, which is typically 1.2 % -1.8 wt% on lean solvent flow rate for BTX feed.

E_CP_0704, edo

8. Hydrocarbon content in Lean SolventIf the feed includes heavier components such as heavy aromatics, it will require higher stripping steam ratio than 2 3 wt%. In addition to the stripping steam rate, the followings can help reduce the hydrocarbon in the lean solvent.Decreasing SRC column pressure Increasing SRC bottom temperature ( not higher than 180 oC ) Increasing EDC Bottom temperature Increasing Solvent to feed ratio

E_CP_0704, edo

Factors affecting Aromatic Purity

The factors affecting aromatic purity at agiven feed rate are: Solvent flowrate EDC / SRC Pressure Water content in Solvent ED Column Feed Temperature ED Column Bottom Temperature Lean Solvent Temperature Reflux Ratio

E_CP_0704, edo

1. Solvent FlowrateThe selective solvent used in the GT-BTX process alters unequally the volatility of the aromatics and non-aromatics, such that non-aromatics are relatively more volatile. An increase in the amount of solvent increases the activity coefficients of non-aromatics more than those of aromatics and thus improves the separation.

E_CP_0704, edo

2. EDC/SRC PressureThe EDC pressure must be controlled to permit condensing the overhead vapors with the water cooler, and reboiling of the bottom using the available heat.Design EDC O/H pressure is 1.2 kg/cm2Higher pressures may result in temperature limitations at the bottom of columnIn general, as the EDC pressure is increased, the aromatic recovery may increase slightly, the aromatic purity decreases slightly, and the utility costs increase slightly.

E_CP_0704, edo

2. EDC/SRC PressureThe SRC pressure is mainly determined by the requirements to have a lower bottom temperature, while effectively stripping the aromatic hydrocarbon.Design conditions are:O/H pressure-0.4 kg/cm2Bottom Temperature175 degC

E_CP_0704, edo

3. Water content in Solvent

In general, water in the solvent directionally improves the extract quality, but is detrimental to the aromatic recovery in the EDC. A small amount of water can be added to the base of the EDC to help in rejecting the non-aromatic from the extract.

E_CP_0704, edo

4. ED Column Feed temperaturethe benzene purity is not greatly affected up to design feed temperature, but then sharply decrease the benzene purity with increase in feed temperature there after.

E_CP_0704, edo

4. ED Column Feed Temperature

E_CP_0704, edo

Chart1

3712611

4173415

4664619

5246226

6068736

72212751

85618674

1790866488

18928138854804

EDC BTM Temperature = Constant; S/F Ratio = 2.2 (by vol) @ 105 C

Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Feed Temperature, oC

Impurities in EDC bottoms stream, wppm

Impurities in EDC Bottoms Stream vs. Feed Temperature

input

Feed Temp.67.0077.0087.0097.00107.00117127137147

Bz Recovery, wt%99.9299.9299.9299.9299.9299.919499.91799.89597.95




Energy, MMKcal/hr26.0525.3724.6823.9723.2522.507621.753917.518410.1467





Reflux (R/(R+D))0.250.250.250.250.250.250.250.250.25

Feed Temp.67.0077.0087.0097.00107.00117127137147

Bz Recovery, wt%100.00100.00100.00100.00100.0010010099.9797.10




Energy, MMKcal/hr25.1624.4823.7823.0722.3421.6120.8616.629.3





Reflux (R/(R+D))0.150.150.150.150.150.150.150.150.15

Feed Temp.67.0077.0087.0097.00107.00117127137147

Bz Recovery, wt%99.7699.7699.7699.7699.7699.7699.7699.73599.213




Energy, MMKcal/hr27.2326.5525.8525.1424.4223.6822.9318.6911.28





Reflux (R/(R+D))0.350.350.350.350.350.350.350.350.35

recovery

recovery

99.996799.92299.76

10099.92299.76

10099.9299.76

10099.9299.76

10099.9299.76

10099.919499.76

10099.91799.76

99.9799.89599.735

97.09697.9599.213


Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Feed Temperature, C

Bz Recovery, wt%

Feed Enthalpy

loss

loss

4.30.490.12

4.30.490.12

4.30.490.12

4.30.490.12

4.30.490.12

4.30.490.12

4.30.490.12

4.30.490.12

4.720.480.12


Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Feed Temperature, C

Solvent Loss, wppm

Feed Enthalpy

energy

energy

25.156726.0527.225

24.47825.3726.5453

23.7824.67825.851

23.0723.968825.14

22.3423.246224.42

21.6122.507623.68

20.8621.753922.93

16.6217.518418.69

9.310.146711.28


Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Feed Temperature, C

Reboiler Duty, MMKcal/Hr

Feed Enthalpy

impurity

impurity

3712611

4173415

4664619

5246226

6068736

72212751

85618674

1790866488

18928138854804


Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Feed Temperature, C

Impurity, wppm

Feed Enthalpy

5. ED Column bottom Temperature

The benzene purity increases with higher than design EDC bottom temperature up to certain range. Typically the benzene purity increases with higher bottom temperature at the cost of higher aromatic content in the raffinate.

E_CP_0704, edo

6. Lean Solvent Temperature

The effect of lean solvent temperature on benzene purity at constant S/F ratio, reflux ratio and various EDC bottom temperature is shown in graph no. 10. Higher solvent temperature at fixed EDC bottom temperature increases the benzene purity.

E_CP_0704, edo

6. Lean Solvent Temperature

E_CP_0704, edo

Chart1

110461800022428

380886613640

21884451

2078175

1974159

S/F Ratio = Constant; Reflux R/(R+D)=0.25

Solvent Temp = 95 C

Solvent Temp=105C

Solvent Temp=110C

EDC Bottom Temperature, oC

Imputiry in Extract, wppm

Impurities in the Extract vs EDC Bottom Temperature @ various Solvent Temperatures

Data

S/F Ratio(Volume basis)2.2035

Reflux (R/(R+D))0.250.250.250.250.250.25

Bz Recovery, wt%100.0098.7196.9695.1089.84

Toluene Recovery, wt%100.00100.00100.00100.00100.00

Overall Recovery, wt%100.0099.7899.4999.1898.29


Energy, MMKcal/hr24.1124.6625.2125.7626.3027.48

Solvent Loss,wppm0.250.260.270.280.290.29


S/F Ratio(Volume basis)2.202.202.202.202.202.20


Reflux (R/(R+D))0.250.250.250.250.250.25

Bz Recovery, wt%100.0099.9299.0989.83

Toluene Recovery, wt%100.00100.00100.00100.00

Overall Recovery, wt%99.9999.8599.6698.29

Impurity in BTM, wppm18,0008,866887874189

Energy, MMKcal/hr22.1622.6923.2523.7924.3325.52





Reflux (R/(R+D))0.250.250.250.250.250.25

Bz Recovery, wt%100.0099.7399.0389.83

Toluene Recovery, wt%100.00100.00100.00100.00

Overall Recovery, wt%100.0099.9599.8498.29

Impurity in BTM, wppm22,42813,6404,451175159225

Energy, MMKcal/hr21.1921.7222.2622.8123.3524.54





Reflux (R/(R+D))0.450.450.450.450.450.45

Bz Recovery, wt%98.9497.2095.3290.6164.71




Energy, MMKcal/hr23.6424.1624.6725.2025.7527.11





Reflux (R/(R+D))0.550.550.550.550.550.55

Bz Recovery, wt%99.9198.5096.5890.6164.72




Energy, MMKcal/hr25.9726.4526.9727.4928.1029.60





impurity

impurity

110461800022428

380886613640

21884451

2078175

1974159

S/F Ratio = ConstReflux R/(R+D)=0.25

Solvent Temp = 95 C

Solvent Temp=105C

Solvent Temp=110C

EDC BTM Temperature, C

Imputiry in Extract, wppm

Impurity vs EDC BTM temp at const solvent temperature

Recovery

118000111

8866

88

78

74

189

Lean Feed BasisSolvent Temp. = 105 C

Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Reflux R/(R+D)=0.45

Reflux R/(R+D)=0.55


Imputiry, wppm

EDC BTM Temperature @ S/F=2.20

11111

Lean Feed BasisS/F(vol./vol.) = 2.40 @ 105 C

Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Reflux R/(R+D)=0.45

Reflux R/(R+D)=0.55


Imputiry, wppm

EDC BTM Temperature @ 2.42 of S/F Ratio

150

99.9988

98.708699.9982100

96.9699.9299.73

95.103599.08999.03

89.8489.8389.83

S/F Ratio =constReflux R/(R+D) =0.25

Solvent Temp= 95C

Solvent Temp=105C

Solvent Temp=110C


Bz. Recovery, wt%

Bz Recovery vs EDC BTM Temp at const solvent temp.

1111

155

16099.9982

16599.92

17099.089

17589.83

Lean Feed Basis Solvent Temp. =105 C

Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Reflux R/(R+D)=0.45

Reflux R/(R+D)=0.55


Bz. Recovery, wt%

EDC BTM Temperature @ 2.20 of S/F ratio

11111

Lean Feed Basis Solvent Temp. =105 C

Reflux R/(R+D)=0.15

Reflux R/(R+D)=0.25

Reflux R/(R+D)=0.35

Reflux R/(R+D)=0.45

Reflux R/(R+D)=0.55


Bz. Recovery, wt%

EDC BTM Temperature @ 2.42 of S/F ratio

7. Reflux Ratio

Effect of various reflux ratios for different solvent feed temperatures on benzene purity is shown in graph no. 14.At constant reflux ratio, increase in solvent temperature helps in aromatic purity.

E_CP_0704, edo

7. Reflux Ratio

E_CP_0704, edo

Chart3

37.75730

28.4145.936040

20.94588.0614492

14.8858.1053059

10.535.71647

7.0721.966245

4.6313.2724

37.7950814

6329.71561704.6

EDC BTM Temp.= Const; S/F Ratio = Const.

Solvent Temp. 95 C

Solvent Temp. 105 C

Solvent Temp. 110 C

Reflux (R/(R+D))

Impurities in EDC bottoms, wppm

Impurities in EDC Bottoms vs. Reflux Ratio

Sheet1

Reflux (R/(R+D))0.150.200.250.300.350.400.450.500.550.600.65


Bz Recovery, wt%100.0099.9799.9299.8599.7599.6799.6399.75100.00




Energy, MMKcal/hr22.3622.7723.2523.7824.4525.1826.0327.0028.20





Reflux (R/(R+D))0.150.200.250.300.350.400.450.500.550.600.65

Bz Recovery, wt%99.9099.8399.7299.5899.4399.2999.1999.3099.8199.99



Impurity in BTM, wppm1821238254342213745933.00

Energy, MMKcal/hr22.3822.7823.2723.7624.4525.1425.9727.0228.2929.761

Solvent Loss,wppm4.301.320.500.240.120.070.040.030.020.0140

Reflux (R/(R+D))0.150.200.250.300.350.400.450.500.550.600.65


Bz Recovery, wt%98.9098.7998.7098.6698.6598.6498.6499.88




Energy, MMKcal/hr24.6224.7325.2125.7626.3727.1227.9828.9530.13





Reflux (R/(R+D))0.150.200.250.300.350.400.450.500.550.600.65

Reflux on Feed( Vol%)11.6815.6120.1025.3231.0038.6746.8056.9469.4684.90

Bz Recovery, wt%99.9899.9499.92100.00


Overall Recovery, wt%100.00100.00100.00100.00100.0099.9999.99100.00100.00100.00

Impurity in BTM, wppm6,0404,4923,0591,6474524147056,15215,913

Energy, MMKcal/hr21.7922.2722.8123.4424.2325.0826.0127.2228.7530.60

Solvent Loss,wppm6.501.750.660.310.160.090.050.030.020.020.01


S/F Ratio(Volume basis)2.202.202.202.202.202.202.202.202.202.202.20


impurity

impurity

37.75730

28.4145.936040

20.94588.0614492

14.8858.1053059

10.535.71647

7.0721.966245

4.6313.2724

37.7950814

6329.71561704.6

EDC BTM Temp.= ConstS/F Ratio = Const.

Solvent Temp. 95 C

Solvent Temp. 105 C

Solvent Temp. 110 C

Reflux (R/(R+D))

Impurity in bottom, wppm

Impurity vs Reflux ratio at const. solvent temp.

recovery

recovery

98.999.999520.15

98.7999.97110.2

98.799.920.25

98.6699.8480.3

98.6599.75140.35

98.6499.6799.9844

98.6499.633199.939


Design

Solvent Temp 95 C

Solvent Temp 105C

Solvent Temp 110C

Reflux, R/(R+D)

Bz. Recovery, wt%

Bz Recovery vs Reflux ratio at const solvent temperature

loss

24.619822.35760.15

24.732422.769921.7929

25.2123.254422.2684

25.755623.778822.806

26.372224.45123.439

27.121425.18424.2267

27.981826.027725.0817

28.952226.997326.014

Design


Solvent Temp. 95 C

Solvent Temp 105C

Solvent Temp. 110C

Reflux, R/(R+D)

EDC Reboiler Duty, MMKcla/Hr

EDC Reboiler Duty vs reflux ratio at const solvent temperature

1.964.091836.5

0.651.237881.75

0.270.482540.659

0.130.234420.3066

0.07460.1180.157

0.0440.06760.085

0.028690.04130.0509

0.02090.0270270.0327

0.0160.01870.02

000.015

0.650.650.0118

EDC BTM Temp = ConstS/F Ratio = Const

Design

Solvent Temp. 95 C

Solvent Temp. 105 C

Solvent Temp. 110 C

Reflux( R/(R+D))

Solvent Loss, wppm

Solvent Loss vs Reflux Ratio

Water Circulation

Raffinate product at the top of the EDC could contain some solvent that must be recovered usually by contact with water. Additional fresh water can be brought to the static mixer 106ME-101 to help facilitate the removal of the solvent. The solvent will separate into the water phase and will be recycled to the water stripper.

E_CP_0704, edo

Water Circulation

The EDC overhead water stream contains some non-aromatic hydrocarbons, which are not desired in the solvent recovery column where could affect the aromatic extract quality. Therefore, this stream needs to be processed in the water stripper by stripping out all hydrocarbon traces.

E_CP_0704, edo

Water Circulation

The water stripper is installed at the top of the steam generator; a small amount of steam is purged out at the top of the stripper together with the stripped non-aromatic hydrocarbon and is sent back to the EDC condenser.

E_CP_0704, edo

Water Circulation

In general, very small quantity of the total water in circulation needs to be stripped overhead to assure that, when the remainder is vaporized and utilized as stripping steam in the SRC, no non-aromatic components will contaminate the extract.

E_CP_0704, edo

Water Circulation

The water is used as stripping steam injected into the bottom of the solvent recovery column, and it helps strip aromatics more easily from solvent by reducing hydrocarbon partial pressure at the SRC bottom. The more stripping steam is injected the fewer hydrocarbons in the lean solvent loop remains.

E_CP_0704, edo

Water Circulation

Typically, the stripping steam ratio will be 1.0 to 3.0 wt% on solvent flow rate. Heavier feed and lower solvent to feed ratio will require more stripping steam.

E_CP_0704, edo

Factors affecting solventlosses and solvent quality The factors which can affect solvent losses and solvent quality are as follows:a.DegradationNeutralization Solvent losses in the raffinated.Solvent losses in the extract

E_CP_0704, edo

a) Degradation During use, the solvent usually turns acidic, though the rate of this process differs widely according to the conditions. The pH number quoted throughout for solvent is measured after 1:1 dilution with water. On this basis, fresh solvent has a pH of approximately 6.

E_CP_0704, edo

a) Degradation The solvent degrades due two primary functions: a. Extreme heat b.Reaction with free oxygen or oxygenates

E_CP_0704, edo

a) Degradation In practice at temperatures up to 200oC, there is no acid formation from solvent in an inert atmosphere. Therefore, at all temperatures practically encountered in an extraction process, acid formation has to be attributed to attack of oxygen.

E_CP_0704, edo

a) Degradation Although the Solvent degradation is minimal up to 200 oC in an inert atmosphere, the SRC bottom temperature should not exceed 180 oC to minimize any potential degradation problem. There are several intermediates leading to polymer and acidic polymer formation, but all are ultimately related to oxygen exposure.

E_CP_0704, edo

a) Degradation These polymers are only partly soluble in solvent and when present in higher concentration, will appear as solid material that must be removed by way of the solvent regenerator. The preferable countermeasure is to avoid oxygen ingress through the feed, solvent and water rerun systems, and vacuum leaks around the SRC.

E_CP_0704, edo

b) Neutralization In order to protect the equipment from corrosion, it is necessary to neutralize any acidic compound that may be formed. Since the intermediate degradation products are sometimes volatile, neutralization of the material in the extractive distillation and recovery columns is required from the top of the tower downward, along with neutralization of the water circulation system.

E_CP_0704, edo

b) Neutralization MEA is one most effective neutralizing agent. Pure solvent in a 1:1 dilution with water shows a pH of 5.8, while the pH of the circulating solvent is normally maintained between 5.5 and 6.0 (in a 1:1 dilution with water).

E_CP_0704, edo

b) Neutralization The MEA dosage can be maintained to keep the solvent pH in this range. It is important not to overdose the system with MEA as MEA could itself be corrosive. The pH of the water circulation loop should also be maintained by MEA addition, keeping the pH between approximately 6.5 and 7.5.

E_CP_0704, edo

b) Neutralization The MEA salts formed are not completely stable and can decompose at high temperatures (e.g. in the solvent recovery column). However, since both the acidic compounds and MEA are volatile, they will recombine in the top condensing area to form neutral salts. Thus, both phases need to be considered for any pH control program.

E_CP_0704, edo

b) Neutralization The major cause of solvent degradation is the influence of oxygen. If oxygen ingress could be completely prevented, regeneration of solvent would probably be eliminated. All extraction plant corrosion, fouling, and the solvent appearance concerns can in most cases be traced back to changes in oxygen intake via a feed system or vacuum leaks.

E_CP_0704, edo

b) Neutralization Process losses of solvent may be to the raffinate, the extract, or the regenerator bottoms. The last is related to the draw off of decomposition products, the formation of which is largely controlled by excluding air from the feed and preventing air leaks into the plant.

E_CP_0704, edo

c) Solvent Losses in the Raffinate The GT-BTX unit has been designed to have very little solvent going to the overhead of the EDC. The solvent has a low volatility and therefore goes to the tower bottoms. However, there may be a small quantity of solvent entrained into the overhead vapors.

E_CP_0704, edo

c) Solvent Losses in the Raffinate Thus, the solvent losses to the raffinate can be controlled as follows: Avoidance of solvent in the overhead by using hydrocarbon reflux and temperature adjustments. Directionally, a higher reflux rate and lower solvent temperature will reduce solvent in the raffinate.

E_CP_0704, edo

c) Solvent Losses in the Raffinate Graph no. 3 shows the solvent losses in the raffinate at a constant EDC bottom temperature with constant S/F ratio with various feed temperatures.

E_CP_0704, edo

c) Solvent Losses in the Raffinate

E_CP_0704, edo

c) Solvent Losses in the Raffinate Graph no. 11 shows the solvent losses at various solvent temperatures with various reflux ratios (R/(R+D)).

E_CP_0704, edo


E_CP_0704, edo

c) Solvent Losses in the Raffinate The larger the reflux ratio is, the less solvent losses become. The solvent losses tend to decrease as the lean solvent temperature decreases. The solvent losses due to higher solvent temperature can be compensated for by properly increased reflux.

E_CP_0704, edo

c) Solvent Losses in the Raffinate Phase separation of the solvent into the water phase in the overhead accumulator system. The distribution of solvent into water is approximately 100 times greater than into non-aromatic hydrocarbons.

E_CP_0704, edo

c) Solvent Losses in the RaffinateWash water can be recirculated around the EDC overhead receiver, through a static mixer in order to enhance the water-hydrocarbons contact. Fresh makeup water mixed with SRC ovhd vapors as necessary and thus makeup water added to the system.The tendency of solvent losses with the ratio of H2O / HC is shown in graph no. 9.

E_CP_0704, edo


E_CP_0704, edo

Chart1

2.52456758555.536229810211.887259198323.6230883431

1.59352138373.49648523447.512118339414.9381293935

1.16518503942.55660292995.491566351310.9237483678

0.91727332892.01359400434.32763339128.6107285313

0.75750800441.66133042373.71745935217.1053356467

0.64457044741.41366912913.03899332826.0497790974

0.56055592321.23061512872.64557211085.2659058794

0.49720070831.08909438892.34122739554.6616702738

0.44486379170.97680075842.100720844.1821417712

0.40354517320.88604289271.90475253553.7931743789

Solvent Temp. & S/F : Constant; Reflux rate : const

10 wppm of solvent in Mixer feed

25 wppm of solvent

50 wppm of solvent

100 wppm of solvent

H2O/HC mole Ratio(@ EDC Ovhd. Receiver)

Solvent Content in Raffiante, wppm

Solvent Content in the Raffinate vs. H20/HC mole ratio

raff

55907

0.6362

8 wpm8 wpm102550100

HC MoleH2O MoleHC/ H2O Mole Ratioefficiency

8641000.1282.3%0.82.012.525.5411.8923.620.3

8642000.2488.8%0.821.271.593.507.5114.940.4

8643000.3691.8%0.840.931.172.565.4910.920.5

8644000.4893.6%0.860.730.922.014.338.610.6

8645000.6094.7%0.880.600.761.663.727.110.7

8646000.7295.5%0.90.510.641.413.046.050.8

8647000.8496.1%0.920.450.561.232.655.270.9

8648000.9696.5%0.940.400.501.092.344.661

8649001.0896.9%0.960.360.440.982.104.181.1

86410001.2097.2%0.980.320.400.891.903.791.2

raff

0

0

0

0

0

0

0

0

0

0

Solvent Temp. & S/F : Const.Reflux rate : constDesign H2O/HC mole ratio : 0.35

Solvent removal rate, wt%

HC / H2O Mole Ratio

Solvent removal rate through the Mixer

0000

0000

0000

0000

0000

0000

0000

0000

0000

0000

Solvent Temp. & S/F : Const.Reflux rate : constDesign H2O/HC mole ratio : 0.35

10 wppm of solvent in Mixer feed

25 wppm of solvent

50 wppm of solvent

100 wppm of solvent

H2O/HC mole Ratio

Solvent in Raffiante, wppm

Solvent Content in the Raffinate

d) Solvent Losses in the Extract

The primary control parameter for solvent losses in the SRC overhead is the column reflux. The top tray vapor from the solvent recovery column contains pure aromatic, water, (that originated as steam in the base of the column), and potential traces of solvent. This mixture is condensed and separated into an aqueous phase and a hydrocarbon phase.

E_CP_0704, edo

d) Solvent Losses in the ExtractPart of the hydrocarbon phase is withdrawn as extract, and part is returned to the top of the column as reflux to reduce the amount of solvent in the overhead. As in the EDC, the small amount of solvent which does go overhead will distribute between aqueous and hydrocarbon phases. Any solvent in the extract will be lost in the fractionation, while any solvent in the aqueous phase will be recovered in the system.

E_CP_0704, edo

d) Solvent Losses in the ExtractThe solvent content of the overhead can never be reduced to zero, so the optimum loss must be based on economic considerations. The higher the reflux/extract ratio, the lower the loss and the higher the utility consumption.

E_CP_0704, edo

d) Solvent Losses in the ExtractA second possibility for solvent losses in extract product is caused by entrainment from the flashing feed. The SRC column has been designed to minimize entrainment, but it is possible to further reduce this tendency by -Increasing SRC column pressure Decreasing SRC bottom temperatureLowering EDC Bottom temperature Decreasing stripping steam rateDecreasing solvent to feed ratiosubject to other conditions.

E_CP_0704, edo

SUMMARYMajor changes Solvent/Feed ratioTrim changes EDC bottoms temperatureRefluxMaintain clean solventSRC bottoms temperatureStripping steamRecycle to feed tank either BOTH raffinate and extract, or NONE

E_CP_0704, edo

Documents

gTC Lidong Training.ppt