Amine Plant Energy Requirements & Items impacting the SRU 10 - - PowerPoint PPT Presentation

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

Amine Plant Energy Requirements & Items impacting the SRU

10 October 2016

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

2

Agenda

AGRU energy needs Amine energy requirements – Regeneration – Processing effects Leanness required – Determine required leanness – Over stripping Energy sources – In amine system – Sulphur conversion waste heat loss due to AGRU SRU energy supply Waste heat – Reactor – Incinerator in excess of SRU/TGT needs, Is there more to save?

Optimisation dependent on operating conditions All quoted figures are indicative

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

3

500 1,000 1,500 2,000 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Typical Solvent loading (mol/mol) Pressure (mbara)

Equilibrium partial pressure of H2S

Typical amine solvent

Amine closed system – chemical reaction

The amine solvent loading is set by temperature and partial pressure of H2S and CO2 in a certain %wt amine solvent, determined by equilibrium, kinetics and the mass transfer between gas and liquid phase

Absorption Low temp, high - low pressure Low solvent equilibrium partial pressure at solvent inlet, mass transfer of the acid components from gas to solvent phase, kinetics role Regenerator temperature, typical 115 °C < T < 140 °C Regenerator pressure, typical 1.5 < p < 2.5 bara Regeneration Operation: High temp, low pressure High solvent equilibrium partial pressure at solvent inlet , mass transfer acid component from solvent to gas phase Absorber temperature, typical 30 °C < T < 65 °C Absorber pressure, typical 1.1 < p < 100 bara

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

4

Amine energy consumers

Solvent regeneration heat

Reboiler steam 75 – 95 % of energy consumption in amine system

• Several components require energy (heat)
• Desorption
• Heating of solvent to regenerator bottom condition
• Internal generation of steam in regenerator reboiler

Heating medium: low pressure steam, also because of the constraint of thermal degradation of the amine at high temperature

Solvent circulation pumps

Remainder of total energy consumption depending on pressure differential and solvent properties Air cooling is a minor energy consumer compared to other energy consumers

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

5

Amine – energy generation

500 1,000 1,500 2,000 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Solvent loading (mol/mol) Pressure (mbara) Typical amine solvent

Amine type kJ/kmol H2S kJ/kmol CO2 60%wt DGA 54 99 50%wt MDEA 40 70

Equilibrium partial pressure of H2S

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

6

Feed gas Sweet gas Lean solvent

Msweet, Cpsweet, Tsweet heat of absorption Mlean, Cplean, Tlean Mfeed, Tfeed, Cpfeed Mrich, Cprich, Trich

Absorber Heat (Enthalpy) Balance

Rich solvent

Heat of absorption (energy make) determined by:

• Solvent type
• Cp (for energy balance)
• Amine type
• Solvent %wt amine
• Type of treating
• selectivity
• ther components removal
• Feed gas pressure
• Feed gas composition - Cp
• Lean solvent temperature
• prevention HC condensation criteria
• Feed gas acid content
• Sweet gas specification

In principle independent of type of internals unless heat distributions is hampered The maximum temperature is usually above the bottom tray

Heat of absorption is larger when the loading is smaller, thus not a constant!

Trich > Tsweet

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

7

Amine – energy consumption for regeneration

500 1,000 1,500 2,000 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Solvent loading (mol/mol) Pressure (mbara) Typical amine solvent

Amine type kJ/kg H2S kJ/kg CO2 60%wt DGA 1570 1972 50%wt MDEA 1045 1340

Equilibrium partial pressure of H2S

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

8

Amine Regeneration (Heat) Enthalpy balance

Heat for regeneration determined by:

• Solvent type
• Cp (for energy balance)
• Amine type
• Rich solvent loading and temperature

after flash and L/R HE

• Solvent %wt amine
• Solvent boiling temperature reboiler
• Type of treating
• selectivity
• ther components removal
• Regenerator bottom pressure
• Downstream unit pressure drop
• Type of internals
• Sweet gas specification
• Reflux temperature

Hydraulic constraint at regenerator inlet due to flashing and flow pattern may limit

Overstripping causes corrosion/erosion Lean solvent Acid gas/steam Rich solvent Reflux H2S

Two phase

Generated steam LP steam Condensate

All streams:

Mstream, Tstream, Cpstream

Stripped solvent Lean solvent

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

9

Steam requirements regenerator

Lean solvent Top steam Rich solvent Reflux

Two phase

LP steam Condensate Ss = sensible heat heating solvent to bottom temperature Sr = heat of reaction chemical desorption of H2S, CO2,

• ther

St = top steam for sufficiently low acid partial pressure in the lean solvent at feed tray, minimum applied by process vendors

Sb = bottom steam (kg/m3) = St + Ss + Sr

minimum applied by process vendors

Sb

CO2, H2S

Sr = (CO2) ∆Hr,CO2 + (H2S) ∆Hr,H2S

Steam

St Ss = Cp∆T

The required solvent leanness is determined by the sweet gas specification

+

∆Hr Cp T P

Bottom steam

reaction heat specific heat temperature pressure

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

10

Regenerator Bottom Temperature

• The regenerator bottom temperature is

determined by the amount of steam generated in the reboiler, which is a boiling aqueous amine at the bottom pressure:

• The more steam is generated, the higher the

pressure drop (∆P) across the regenerator trays, more gas phase

• The higher the pressure drop, the higher the

regenerator bottom pressure (P0 + ∆P)

• The higher the bottom pressure, the higher

the bottom temperature

• NB similar effect due to the stripping of acid

gas in the reboiler is very small, because the solvent leanness should be met at the stripping stage

• Reboiler external steam regenerator steam

Lean solvent Acid gas/steam Rich solvent Reflux H2S + CO2 + steam

Two phase: Flashed H2S and CO2 separates at feed inlet

LP steam Condensate Stripping stage

P0 + ΔP P0

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

11

AGRU internal energy saving

FEED GAS FLASH GAS

SWEET GAS HEAT IN SRU FEED

Inside AGRU Turbo expander High pressure absorber only Not on one shaft with solvent pump Saving on pump power dependent on pressure difference

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

12

AGRU internal energy saving

FEED GAS FLASH GAS

SWEET GAS HEAT IN SRU FEED

Inside AGRU Lean/rich heat exchanger Optimisation limited by:

• Regeneration needs (see leanness)
• Type of heat exchanger
• Use of low pressure steam limitation
• Solvent loading (flashing in HE)
• Fouling system
• System configuration (vibration due

to 2 phase flow in vertical regenerator inlet piping)

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

13

AGRU and SRU interfaces

H2S + ½O2 S + H2O H2S + R3N HS- + R3NH+

WASTE HEAT

(Steam generation)

AIR

FEED GAS FLASH GAS

SWEET GAS HYDROCARBON and CO2

IN AMINE SOVENT

HEAT IN

TAIL GAS ANALYSER

TO DEGASSER SRU FEED

Outside AGRU affecting SRU

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

14

Entrained and soluble hydrocarbon route

WASTE HEAT

(Steam generation)

AIR

FEED GAS FLASH GAS

SWEET GAS

HYDROCARBON IN AMINE SOVENT

HEAT IN

TAIL GAS ANALYSER

TO DEGASSER

When the color is more intensive, there is more entrained than soluble rated hydrocarbon in the stream

SRU FEED

Hydrocarbon combustion consumes energy in the SRU

Hydrocarbon in acid gas

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

15

SRU affected by hydrocarbon from amine unit

Hydrocarbon content in SRU feed gas – Preferably below 1%vol – Maximum 5% vol

• Air consumption increase thus

– Reduction maximum capacity – Therefore the overall Sulphur conversion

• Energy consumption increase

However Fast composition changes cannot be controlled by analysers due to dead time

This can be handled by Tail gas analyser when change is slow

Hydrocarbon composition fluctuation Unburned liquid and heavy HC form soot on catalyst Black Sulphur Can even block Sulphur rundown

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

16

Co-absorption of CO2 – selective treating

H2S + ½O2 S + H2O H2S + R3N HS- + R3NH+

WASTE HEAT

(Steam generation)

AIR

FEED GAS FLASH GAS

SWEET GAS

HYDROCARBON IN AMINE SOVENT

HEAT IN

TAIL GAS ANALYSER

TO DEGASSER SRU FEED

H2S

CO2

Ratio

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

17

CO2 co-absorption determining parameters

CO2 co-absorption reduction design parameters based on:

• Chemical equilibrium differences H2S and CO2

– Meeting equilibrium would require infinite # trays/packing height – Competition H2S and CO2 – Equilibrium condition dependent

• Reaction kinetics

– H2S has a very fast reaction at the gas phase – CO2 has a slow reaction in the liquid bulk, BUT

• CO2 accelerator, even in minimum amount, destroys selectivity
• Gas/Liquid mass transfer

– Type of absorber internals – gas/liquid interface, residence time

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

18

H2S/CO2 ratio

Reduction of CO2 co-absorption

Optimise DESIGN/DEBOTTLENECK based on realistic operating window, may be seasonally different Solvent selection and concentration Absorber temperature (different effect at high and low pressure) Flash vessel temperature and pressure Include sufficient on-line stream analysers for main components, include logic in control based on simulations based on operating experience Select the best practice internals to reduce entrainment (as with hydrocarbon) Optimise OPERATION within the equipment constraints in an existing plant Awareness of the contributing operational conditions is beyond pressure and temperature in an amine unit slow and smooth operational changes can be applied, opening on the run optimisation (based on modeling) Check if conditions change (new wells) and find new optimum process simulation may help, but mostly is not refined enough

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

19

AGRU operation trends affect energy demand

FEED GAS FLASH GAS

SWEET GAS HEAT IN SRU FEED

Inside AGRU Parameter trends in next slides

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

20

Energy influencing trends

Solvent variables

%wt amine, heat of reaction

Feed gas H2S and CO2 Accelerator CO2 removal

Accelerator effectiveness

Deeper spec H2S Deeper spec CO2

Integration AGRU/TGT/AGE

%wt amine, Cp %wt amine, Cp Mercaptan removal

Hybrid solvent swap

Type of amine, prim, sec, tert

No trend

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

21

Energy influencing trends

Operating variables

Operating pressure absorber

AGRU

Operating pressure absorber

AGE

Operating pressure absorber

TGT

Lean solvent temperature

Total removal, High pressure

Lean solvent temperature

Selective H2S removal, Low pressure

Lean solvent temperature

Selective removal, High pressure

Lean solvent temperature

Selective removal, High pressure

Operating pressure regenerator Pressure drop regenerator

Rich solvent inlet temperature regenerator, limit bottom Rich solvent inlet temperature regenerator, limit top

Neutral

High loading

Rich solvent inlet temperature regenerator, limit bottom

Neutral

Low loading

External steam flow

Risk of overstripping

External steam temperature

Risk of overstripping and degradation

High Sulphur Recovery (TGT) Foaming tendency Retrograde HC condensation Solvent quality STEADY OPERATION Trays or packing regenerator

Trays

Trays or packing regenerator

Trays

Solvent rich loading

Bottom limit

Material integrity (corrosion)

Case dependent

Regenerator overhead temperature Regenerator reflux temperature

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

22

Energy influencing trends

Hardware

Trays or packing absorber

Trays

Trays or packing regenerator

Trays

Isometrics, pressure drop Turbo expander

Header system between processes

Type of HE, pressure drop Trays or HE, approach Case dependent Effective mechanical filter

Effective activated carbon filter + mechanical after filter

More, other? Plant and condition specific Operational models can help explore options

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

23

Conclusion

AGRU design, operation and installed hardware should take into account its impact on the SRU Amine units have many parameters to

• ptimise its operation. Indicative trends are

presented and can be used without violating Amine unit specification Integrated design and operation offer energy saving options Know your processes – trends depend on conditions

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

24

Discussion

Which do you use?

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

25

Thank you

ABU DHABI GAS INDUSTRIES (GASCO)

GASCO presentation MESPON 2016

26

References

Reaction heat quotes averaged from

• Merkley, K.E., Christensen, J.J., Izatt, R.M., 1987, ‘Enthalpies of Absorption of Carbon Dioxide in Aqueous

Methyldiethanolamine Solutions’, Thermochimica Acta, vol. 121, pp. 437-446.

• Kohl, A., Nielsen, R., 1997, ‘Gas Purification’, Gulf Publishing Company, Houston Texas.
• Versteeg, G.F., van Swaaij, W.P.M. 1988, 'Solubility and Diffusivity of Acid Gases (CO2, N2O) in aqueous

Alkanolamine solutions', Journal of Chemical engineering data, vol. 33, pp 29-34.

• Oscarson, R.H., van Dam, R.H., Izatt, R.M., 1990, ‘Enthalpies of Absorption of Hydrogen Sulfinolide in Aqueous

Methyldiethanolamine Solutions’, Thermochimica Acta, vol. 170, pp. 235-241.

• Oilfield Processing of Petroleum, Natural Gas, Volume 1