Chemical Reactors Energy Integration Applied to Supercritical Water Oxidation

1
Chemical Reactors Energy Integration Applied to
Supercritical Water Oxidation

• E.D. Lavric1,3, H. Weyten2, J. De Ruyck3, V.
  Plesu1, V. Lavric1

1University Politehnica of Bucharest-CTTIP 2Vlaams
e Instelling vor Technologisch Onderzoek 3Vrije
Universiteit Brussel
2
Supercritical water oxidation (SCWO) main
features

• The SCWO technology is an efficient, economical,
  and environmentally safe method to destroy a
  significant share of the aqueous wastes
• SCWO is a homogeneous-phase process that occurs
  in water at temperatures and pressures above the
  mixture thermodynamic critical point (for water
  22.1 MPa and 647 K).

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Problems to be solved before starting the analysis

• Units topology of the process
• Type of the chemical reactor
• Kinetics of the SCWO oxidation
• Package of properties to be used

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Main parameters of the process

• Pressure (between 24-50 MPa)
• Temperature of the reactor feed (gt 650 K)
• Pollutant concentration
• Maximum allowable temperature 925 K
• Destruction efficiencies of over 99.99

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Type of the chemical reactor

• Perfectly mixed
• Plug flow
• Adiabatic
• Non-adiabatic

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SCWO Flowsheet
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Parameters

• Organic concentration 1.67 (n-C6H14) Tout r
  893 K
• Pressure 23 MPa
• Destruction efficiency over 99.99 (?length
  reactor)
• Mixer input temperatures
• 673 K (adiabatic reactor)
• 683 K (non-adiabatic)
• 693 K (non-adiabatic)
• 703 K (non-adiabatic)
• 713 K (non-adiabatic)
• 723 K (non-adiabatic).
• Package of properties Peng Robinson with
  modified Huron-Vidal mixing rules

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Kinetics of oxidation

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Pinch Analysis - basics

• Identifies
• sources (hot streams)
• sinks (cold streams)
• Builds
• composite hot and cold stream curves
• grand composite curves
• problem table
• Designs
• HEN topology avoiding heat transfer across the
  pinch
• Economically optimum configuration - transfers
  some heat across the pinch, breaking loops
  accordingly

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Chemical Reactors Energy Integration (CREI)
Analysis - Basics

• Identifies
• heat generated by the chemical process
• reversible reaction temperature
• Builds
• virtual heat exchangers
• Designs
• optimal plant topology, through extended pinch
  analysis

Trev reversible temperature (no entropy) T
actual working temperature dqchem heat of
chemical process dq heat exchanged with the
surroundings
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ImplementationA) Reversible Temperature
Computation

• zero order approach
• Trev is computed for the entire chemical reactor
• first order approach
• (Trev) in is computed considering an infinitely
  small advancement of the chemical process at
  entrance
• (Trev) out is computed following the same
  procedure, but for the exit conditions.

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B) Reactor Replacement Adiabatic (exo case)
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Guideline from Chemical Reactors Energy
Integration (CREI) Analysis

• The CREI analysis guideline emerged from
  previous works states to heat up as much as
  possible the input of the chemical reactor for
  exothermic processes using if possible some low
  value utilities or a part of the generated heat
  and to generate as much as possible high grade
  utility.

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SCWO Flowsheet
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Balanced composite curvesPinch
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Pinch Analysis Flowsheet, 673 K
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Balanced Composite Curves for Chemical Reactors
Energy Integration (CREI)
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CREI Flowsheet, 673 K
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Pinch Analysis Flowsheet T gt 673 K
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CREI Flowsheet, T gt 673 K
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Conditions to be fulfilled for non-adiabatic
cases

• The imposed inlet temperature of the pollutant in
  the mixer
• The length of the reactor used for the chemical
  process (active length)
• Pinch both
• CREI one

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Generated Entropy
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Conclusions

• Applying CREI first gives the same scheme with
  the cascade pinch/CREI
• The generated entropy has practically the same
  value after the CREI analysis or after pinch/CREI
  analysis
• An adiabatic operation of the reactor is
  desirable
• A better energy-power integration could be done
  using a supercritical turbine or an Organic
  Rankine Cycle

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Acknowledgements
This work is the result of the cooperation
between VITO, VUB and UPB-CTTIP developed under
the auspices of the bilateral agreement between
the Flemish and the Romanian governments BIL
031326 - Application of chemical pinch technology
in process industries.