water management in process plants

Water Management in Process Plants

David PuckettDébora Campos de Faria

Miguel J. Bagajewicz

Sources of Refinery Wastewater

Caustic Treating

Distillation

Amine Sweetening

Merox Sweetening

Hydrotreating

Desalting

NH3 and H2S Water Contamination

Water Contamination with Organics

NH3 and H2S Water Contamination

Water Contamination with NH3, H2S, and Organics

Saline Water Contamination

Water Management Methods Wastewater produced in industrial processes

can be handled in three fashions.

End-of-Pipe Cleanup

Regeneration

Regeneration Methods API separator and activated carbon to

remove organics from distillation and hydrotreating wastewater.

Reverse osmosis to removesaline contamination from desalting wastewater.

Chevron wastewater treatment to remove acid gas contamination from caustic treating, sweetening, and hydrotreating wastewater.

Wastewater Optimization Current methods of optimizing water reuse

and regeneration rely on several assumptions.

Operating and capital costs are functions solely of treated water flow rate.

Fixed process outlet concentrations.

Wastewater Optimization

22% of the amount of contaminant removed,89% of the FCI

51% of the amount of contaminant removed,78% of the FCI

$458000

$408000

$317000

Wastewater Optimization Depending on the contaminants present and

the treatment processes used, the assumption that regeneration costs are dependent solely on flow rate may not be valid.

The optimum solution for a water allocation problem must take into account factors other than flow rate.

Removal of Organics

Distillation

Hydrotreating

Wastewater Contaminated with Organics

API Separator and Activated

Carbon Adsorber

Wastewater Free of Organics

API Separator Removes multi-phase contamination through

differences in specific gravity.

API Separator Appropriate for use with any contaminant that

forms a distinct phase in the process water.

Oil and Light Organics

Organic and InorganicSediment

API Separator Simulation The basis of the separation

is Stokes’ Law.

For a given contaminant in water, rate of settling is determined solely by contaminant particle size.

Quality of separation can be improved through flocculation and coagulation.

Buoyant Force

Gravitational Force

Drag Force

API Separator Simulation Process water contaminant concentration

does not change quality of separation. Percentage of contaminants removed on a

volume basis determined based on a normal distribution of particle radii.

Quality of Separation vs. Length

Volume Percent of Contaminants Removed

0 10 20 30 40 50 60

Separator Length (m)

Separator Depth = 1 mSeparator Width = 2 mEntrance to Separator at 0.5 mProcess Water Flow Rate = 1 m3 / sContaminant SG = 0.95Mean Contaminant Diameter = 0.5 mm

Quality of separation improves with increasing length, but with diminishing returns.

Quality of Separation vs. Specific Gravity

0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

Contaminant SG

Separator Depth = 1 mSeparator Width = 2 mSeparator Length = 25 mEntrance to Separator at 0.5 mProcess Water Flow Rate = 1 m3 / sMean Contaminant Diameter = 0.5 mm

Separation quality is poor for contaminants similar in density to water.

Quality of Separation vs. Particle Diameter

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Contaminant Particle Diameter (mm)

Separator Depth = 1 mSeparator Width = 2 mSeparator Length = 25 mEntrance to Separator at 0.5 mProcess Water Flow Rate = 1 m3 / sContaminant SG = 0.95

Quality of separation improves with increasing particle diameter, but with diminishing returns.

Quality of Separation vs. Wastewater Velocity

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Wastewater Velocity (m/s)

Separator Depth = 1 mSeparator Width = 2 mSeparator Length = 25 mEntrance to Separator at 0.5 mContaminant SG = 0.95Mean Contaminant Diameter = 0.5mm

Quality of separation improves with decreasing velocity. A velocity of zero would give perfect separation.

Quality of Separation vs. Settling Distance

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Height of Separator Entrance (m)

Separator Depth = 1 mSeparator Width = 2 mSeparator Length = 25 mContaminant SG = 0.95Process Water Flow Rate = 1 m3 / s

Quality of separation improves with decreasing settling distance. Separators that handle oil will have entrance as close to water surface as possible.

Equipment Cost vs. Flow rateEquipment Cost for API 40 Oil Removal

$2,000.00

$4,000.00

$6,000.00

$8,000.00

$10,000.00

$12,000.00

$14,000.00

0 0.2 0.4 0.6 0.8 1

Flow Rate (m3 / s)

75% Drop in Concentration85% Drop in Concentration95% Drop in Concentration98% Drop in Concentration99% Drop in Concentration99.5% Drop in Concentration

Separator Depth = 1 mSeparator Width = 2 mMean Particle Diameter = 1 mmProcess Water Flow Rate = 0.5 m3 / s

Equipment cost is sensitive to both flow rate and separation quality.

Operating Cost vs. Flow rateOperating Cost for API 40 Oil Removal

$20,000.00

$40,000.00

$60,000.00

$80,000.00

$100,000.00

$120,000.00

0 0.2 0.4 0.6 0.8 1

Flow Rate (m3 / s)

Separator Depth = 1 mSeparator Width = 2 mMean Particle Diameter = 1 mmProcess Water Flow Rate = 0.5 m3 / s

Operating cost is sensitive only to flow rate.

API Separator Performance With a normal distribution of particle

diameters, quality of separation can be solved analytically.

A bit impractical to implement.

API Separator Performance

Varying h

Varying L

Varying SG

Varying Dp Varying F/A

The approximation is quite close for all variables. The worst fit is for changes in settling height.

API Separator Equipment Cost

Equipment cost is dependent on flow rate, quality of separation, specific gravity of contaminant, contaminant particle size, settling distance, and the price of steel.

Varying F and %QS

Varying ΔSG, Dp, h

API Separator Operating Cost

Operating cost is dependent solely on flow rate.

Activated Carbon Removes soluble contaminants through

adsorption onto the activated carbon surface.

Activated Carbon Appropriate for use with liquid or gaseous

contaminants that are water soluble or form emulsions.

Dissolved Organics

Insoluble Organics of < 150 micronsDroplet Size

Dissolved Gases

Activated Carbon Simulation Separation will follow the

Langmuir isotherm.

For the Langmuir isotherm, the rate of adsorption, assuming negligible pore holdup and spherical adsorbate particles, is as follows.

CKCKNNII

IIISI 1

rrdCdNt

Activated Carbon Simulation For a fixed bed adsorber,

process water should reachequilibrium with activatedcarbon prior to end of bed.

A constant length of bedis required for adsorption.

Water Treatment Rate vs. Adsorbant Surface Area

Activated Carbon Adsorption

10152025303540

200 700 1200 1700 2200

Adsorbant Surfac e Area (m2 / kg)

Contaminant Diffusivity = 5 * 10 ^ -11 m2 / sLangmuir Coefficient = 0.06 m3 / kgSaturation Adsorption = 0.4 kg / kg adsorbantInlet Contaminant Concentration = 0.25 kg / m3

Greater adsorbant surface area results in faster adsorption and a faster rate of treatment.

Time in Service vs. Adsorber Diameter

0200400600800

1000120014001600

0 0.5 1 1.5 2

Adsorber Diameter (m)

) Contaminant Diffusivity = 5 * 10 ^ -11 m2 / sLangmuir Coefficient = 0.06 m3 / kgSaturation Adsorption = 0.4 kg / kg adsorbantInlet Contaminant Concentration = 0.25 kg / m3

A greater diameter has more adsorbant per unit length and thus will take longer to saturate.

Time in Service vs. Adsorber Height

0 5 10 15 20 25

Adsorber Height (m)

The saturation wave travels through the adsorber at a constant speed.

Outlet Concentration vs. Inlet Concentration

0 0.2 0.4 0.6 0.8 1

Inlet Conc entration (kg / m3)

Contaminant Diffusivity = 5 * 10 ^ -11 m2 / sLangmuir Coefficient = 0.06 m3 / kgSaturation Adsorption = 0.4 kg / kg adsorbant

Outlet concentration from adsorber is dictated by adsorption thermodynamics.

Equipment Cost vs. Flow Rate

$2,000.00

$4,000.00

$6,000.00

$8,000.00

$10,000.00

$12,000.00

0 5 10 15 20 25

Flow Rate (m3 / hr)

Wastewater pump and column diameter must scale for flowrate.

Operating Costs vs. Flowrate

$50,000.00

$100,000.00

$150,000.00

$200,000.00

$250,000.00

0 5 10 15 20 25

Flow Rate (m3 / hr)

A greater flow rate means more regenerations per year in addition to increased pumping work.

Equipment Cost vs. Inlet Concentration

$2,000.00

$4,000.00

$6,000.00

$8,000.00

$10,000.00

0 0.2 0.4 0.6 0.8 1

Contaminant Diffusivity = 5 * 10 ^ -11 m2 / sLangmuir Coefficient = 0.06 m3 / kgSaturation Adsorption = 0.4 kg / kg adsorbantInlet Contaminant Flow Rate = 7.035 m3 / hr

No changes in the adsorber need to be made to accommodate a greater inlet concentration.

Activated Carbon Aerogel

$50,000.00

$100,000.00

$150,000.00

$200,000.00

$250,000.00

0 0.2 0.4 0.6 0.8 1

Contaminant Diffusivity = 5 * 10 ^ -11 m2 / sLangmuir Coefficient = 0.06 m3 / kgSaturation Adsorption = 0.4 kg / kg adsorbantInlet Contaminant Flow Rate = 7.035 m3 / hr

A greater inlet concentration has the same effect as a greater flow rate. More contaminant must be adsorbed necessitating more regenerations.

Activated Carbon Performance Outlet concentration can be calculated

analytically.

Activated Carbon Equipment Cost

Equipment cost is dependent on flow rate, inlet concentration, column measurements, and the prices of steel and activated carbon.

Varying F and CIN

Varying D Varying H

Activated Carbon Operating Cost

Operating cost is dependent only on flow rate and concentration.

Varying F

Varying CIN

Removal of Salts

DesaltingWastewater

Contaminated with Salts

Reverse Osmosis

Separation

Wastewater Free of Salts

Reverse Osmosis Removes salts from process water by forcing

water against the salt concentration gradient.

Reverse Osmosis Suitable for the removal of any soluble

contamination.

Soluble Salts

Soluble Organics

Microorganisms

Reverse Osmosis Simulation Separation proceeds based

on Fick’s First Law.

For reasonably dilute solutions, the van’t Hoff approximation of osmotic pressure can be used.

Quality of separation is fixed by type of membrane used.

Flow Rate vs. Membrane Area

Purified Water Flow Rate

0.0005

0.0015

0.0025

0.0035

0 50 100 150 200 250 300 350 400 450 500

Membrane Area (m2)

Membrane Thickness = 0.002 mMembrane Permeability = 1.92 * 10-9 ((m3 m) / (m2 sec atm))Brine Pressure = 10 atmBrine Ion Concentration = 100 mol / m3

Ion Rejection Percentage = 0.99

Flow rate and membrane area are linearly related, as would be expected from Fick’s Law.

Flow Rate vs. Membrane Thickness

0 0.0005 0.001 0.0015 0.002

Membrane Thickness (m)

Membrane Area = 100 m2

Membrane Permeability = 1.92 * 10-9 ((m3 m) / (m2 sec atm))Brine Pressure = 10 atmBrine Ion Concentration = 100 mol / m3

Flow rate and membrane thickness are inversely related, as would be expected from Fick’s Law.

Flow Rate vs. Brine Pressure

-0.0004-0.0002

00.00020.00040.00060.00080.001

0.00120.0014

1 3 5 7 9 11 13 15

Brine Pressure (atm)

Membrane Thickness = 0.002 mMembrane Permeability = 1.92 * 10-9 ((m3 m) / (m2 sec atm))Brine Ion Concentration = 100 mol / m3

Flow rate is zero when the pressure gradient is equal and opposite to the osmotic pressure gradient.

Flow Rate vs. Rejection Percentage

00.00010.00020.00030.00040.00050.00060.00070.00080.0009

0.25 0.35 0.45 0.55 0.65 0.75 0.85 0.95

Rejection Percentage

Membrane Thickness = 0.002 mMembrane Permeability = 1.92 * 10-9 ((m3 m) / (m2 sec atm))Brine Pressure = 10 atmBrine Ion Concentration = 100 mol / m3

A higher rejection percentage results in a larger osmotic pressure gradient.

Flow Rate vs. Brine Concentration

-0.0004

-0.0002

0.0002

0.0004

0.0006

0.0008

0 50 100 150 200 250 300 350 400 450 500

Brine Concentration (mol/m3)

Membrane Thickness = 0.002 mMembrane Permeability = 1.92 * 10-9 ((m3 m) / (m2 sec atm))Brine Pressure = 10 atmIon Rejection Percentage = 0.99

Again, flow rate is zero when the pressure gradient is equal and opposite to the osmotic pressure gradient.

Flow Rate vs. Temperature

0.000610.0006150.00062

0.0006250.00063

0.0006350.00064

0.0006450.00065

0.000655

273 278 283 288 293 298 303 308 313 318 323

Temperature (K)

Membrane Thickness = 0.002 mMembrane Permeability = 1.92 * 10-9 ((m3 m) / (m2 sec atm))Brine Pressure = 10 atmBrine Concentration = 100 mol/m3

The van’t Hoff approximation introduces a dependence of osmotic pressure on temperature.

Equipment Cost vs. Flow Rate at 1463 ppm Inlet

TDS = 50 mol / m3 Equipment Cost

$500,000.00

$1,000,000.00

$1,500,000.00

$2,000,000.00

$2,500,000.00

$3,000,000.00

$3,500,000.00

$4,000,000.00

0 5 10 15 20 25 30 35

Flow Rate (m3 / hr)

80% Rejection

96% Rejection

99.2% Rejection

99.84% Rejection

Inlet = 1463 ppm80% = 293 ppm96% = 59 ppm99.2% = 12 ppm99.84% = 2 ppm

Membrane Thickness = 0.0001 mMembrane Permeability = 9.17 * 10-10 ((m3 m) / (m2 sec atm))Brine Pressure = 10 atmBase Ion Rejection Percentage = 0.8

Equipment cost increases exponentially with process water purity as membrane rejection is fixed so membranes must be worked in series to achieve higher purity.

Equipment Cost vs. Flow Rate at 59 ppm Inlet

TDS = 2 mol / m3 Equipment Cost

$500,000.00

$1,000,000.00

$1,500,000.00

$2,000,000.00

$2,500,000.00

$3,000,000.00

$3,500,000.00

$4,000,000.00

0 5 10 15 20 25 30 35

Flow Rate (m3 / hr)

80% Rejection

96% Rejection

99.2% Rejection

99.84% Rejection

Inlet = 59 ppm80% = 12 ppm96% = 2 ppm99.2% = 0.5 ppm99.84% = 0.09 ppm

Equipment costs are dependent on the relative inlet/outlet concentrations, not the absolute concentrations.

Operating Cost vs. Flow Rate at 1463 ppm Inlet

TDS = 50 mol / m3 Operating Cost

$200,000.00

$400,000.00

$600,000.00

$800,000.00

$1,000,000.00

$1,200,000.00

$1,400,000.00

$1,600,000.00

0 5 10 15 20 25 30 35

Flow Rate (m3 / hr)

80% Rejection

96% Rejection

99.2% Rejection

99.84% Rejection

Inlet = 1463 ppm80% = 293 ppm96% = 59 ppm99.2% = 12 ppm99.84% = 2 ppm

The same trends as observed in equipment costs are observed in operating costs.

Operating Cost vs. Flow Rate at 59 ppm Inlet

TDS = 2 mol / m3 Operating Cost

$200,000.00

$400,000.00

$600,000.00

$800,000.00

$1,000,000.00

$1,200,000.00

$1,400,000.00

$1,600,000.00

0 5 10 15 20 25 30 35

Flow Rate (m3 / hr)

80% Rejection

96% Rejection

99.2% Rejection

99.84% Rejection

Inlet = 59 ppm80% = 12 ppm96% = 2 ppm99.2% = 0.5 ppm99.84% = 0.09 ppm

The same trends as observed in equipment costs are observed in operating costs.

Reverse Osmosis Performance Outlet concentration defined by membrane

properties.

Reverse Osmosis Flow Rate

Reverse Osmosis Equipment Cost

Varying F and CIN

Equipment costs are dependent on flow rate, brine concentration, and membrane cost for single membrane. Cost scales based on bypass ratio and number of membranes in series for a series of membranes.

Reverse Osmosis Operating Cost

Varying F

Operating costs are dependent solely on flow rate. Cost scales based on bypass ratio and number of membranes in series for a series of membranes.

Removal of H2S and NH3

Wastewater Contaminated with H2S and

Chevron Wastewater Treatment

Wastewater Free of H2S and NH3

Caustic Treating

Amine Sweetening

Merox Sweetening

Hydrotreating

Chevron Wastewater Treatment Removes dissolved gases from wastewater

through stripping and absorption.

Chevron Waste Water Treatment PFD

Ammonia Stripper

Partial Condenser

Ammonia Stream

Water feed

Hydrogen Sulfide Stripper

Hydrogen Sulfide Stream

Partial Reboiler Partial Reboiler

Stripped water

Chevron Wastewater Treatment Suitable for the removal of any suitably

volatile contaminant.

Hydrogen Sulfide

Ammonia

Chevron Wastewater Treatment Simulation

Hydrogen Sulfide - Water Stripping

0 0.01 0.02 0.03 0.04 0.05 0.06

Liquid Mole Fraction Hydrogen Sulfide

m=L/Gb=Yo-XI(L/G)

Equilibrium Line

McCabe-Thiele Method can be used.

Quality of Stripping vs. Reboil Ratio

H2S Stripping

0.0070.00720.00740.00760.0078

0.0080.00820.00840.00860.0088

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Reboil Rati o

Inlet H2S Concentration = 1000 mol/m3Tray # = 6Outlet Gas = 50% H2S

Superior quality of separation achieved with less of the wastewater boiled.

Quality of Stripping vs. Number of Trays

H2S Stripping

1 3 5 7 9 11

Tray Number

Inlet H2S Concentration = 1000 mol/m3Outlet Gas = 50% H2SReboil Ratio = 0.6

Superior separation achieved at greater number of trays, though diminishing returns are noted.

Quality of Stripping vs. Inlet Concentration

H2S Stripping

0.01 0.02 0.03 0.04 0.05 0.06 0.07

Inlet Water H2S %

Inlet H2S Concentration = 1000 mol/m3Outlet Gas = 50% H2SReboil Ratio = 0.6Tray # = 6

An increase in inlet concentration will always increase the outlet concentration if all other factors remain constant.

H2S Stripping

$5,000.00

$10,000.00

$15,000.00

$20,000.00

$25,000.00

$30,000.00

0 10 20 30 40

Flow Rate (m3 / hr)

Inlet Concentration = 0.0146

Outlet Gas = 50% H2SReboil Ratio = 0.6Tray # = 6

Equipment costs increase in stepped fashion based on need for additional tray to maintain specified outlet concentrations.

Operating Cost vs. Flow Rate

H2S Stripping

$0.00$1,000,000.00$2,000,000.00$3,000,000.00$4,000,000.00$5,000,000.00$6,000,000.00$7,000,000.00$8,000,000.00$9,000,000.00

0 10 20 30 40

Flow Rate (m3 / hr)

Outlet Gas = 50% H2SReboil Ratio = 0.6Tray # = 6

Operating costs insensitive to inlet concentration as primary operating costs is heating of large amounts of water.

H2S Stripping

$5,000.00

$10,000.00

$15,000.00

$20,000.00

$25,000.00

$30,000.00

$35,000.00

0 10 20 30 40

Flow Rate (m3 / hr )

Outlet Concentration = 0.012

Same trends as observed with varied inlet concentrations.

H2S Stripping

$0.00$1,000,000.00$2,000,000.00$3,000,000.00$4,000,000.00$5,000,000.00$6,000,000.00$7,000,000.00$8,000,000.00$9,000,000.00

0 10 20 30 40

Flow Rate (m3 / hr)

Same trends as observed with varied inlet concentrations.

Chevron Wastewater Treatment Simulation

Ammonia - Water Distillation

0 0.2 0.4 0.6 0.8 1

Liquid Mole Fraction Ammonia

m=Reflux Ratio

(YI,YI)

McCabe-Thiele Method can be used.

Distillation Quality vs. Number of Trays

NH3 Distillation

1 3 5 7 9 11

Tray Number

3 % Inlet NH3 Concentration = 1000 mol/m3

Outlet Gas = 98% NH3Reboil Ratio = 0.6Reflux Ratio = 0.6

Same trends as observed with stripping column.

Distillation Quality vs. Reboil Ratio

NH3 Distillation

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Reboil Ratio

Inlet NH3 Concentration = 1000 mol/m3Outlet Gas = 98% NH3Reflux Ratio = 0.6Stripping Tray # = 6

Distillation Quality vs. Reflux Ratio

NH3 Distillation

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Refl ux Ratio

Inlet NH3 Concentration = 1000 mol/m3Outlet Gas = 98% NH3Reboil Ratio = 0.6Stripping Tray # = 6

Increasing reflux ratio will improve the quality of the separation. Note the break in the graph at the minimum reflux ratio.

NH3 Distillation

$5,000.00

$10,000.00

$15,000.00

$20,000.00

$25,000.00

$30,000.00

0 10 20 30 40

Flow Rate (m3 / hr)

Outlet Gas = 98% NH3Reboil Ratio = 0.6Reflux Ratio = 0.6Stripping Tray # = 6

NH3 Distillation

$0.00$1,000,000.00$2,000,000.00$3,000,000.00$4,000,000.00$5,000,000.00$6,000,000.00$7,000,000.00$8,000,000.00$9,000,000.00

0 10 20 30 40

Outlet Gas = 98% NH3Reboil Ratio = 0.6Reflux Ratio = 0.6Stripping Tray # = 6

NH3 Distillation

$0.00$5,000.00

$10,000.00$15,000.00$20,000.00$25,000.00$30,000.00$35,000.00$40,000.00

0 10 20 30 40

Outlet Concentration =0.00982

Inlet NH3 Concentration = 1000 mol / m3Outlet Gas = 98% NH3Reboil Ratio = 0.6Reflux Ratio = 0.6

NH3 Distillation

$2,000,000.00

$4,000,000.00

$6,000,000.00

$8,000,000.00

$10,000,000.00

0 10 20 30 40

Flow Rate (m3 / hr)

Inlet NH3 Concentration = 1000 mol / m3Outlet Gas = 98% NH3Reboil Ratio = 0.6Reflux Ratio = 0.6

Performance of Chevron Wastewater Treatment H2S Removal

NH3 Removal

Chevron Wastewater Treatment Equipment Costs

Varying F

Varying Tray Number

Varying D

Equipment costs strongly dependent on number of trays, column diameter, and the price of stainless steel.

Chevron Wastewater Treatment Operating Costs For both the stripping and the distillation

columns, operating costs follow the below relation.

Conclusions Capital costs for API separators are heavily

dependent on inlet/outlet concentration ratio. Operating costs for API separators are independent of concentration.

Capital costs for activated carbon adsorption are independent of concentration. Operating costs for activated carbon adsorption are heavily dependent on concentration.

Conclusions Both capital costs and operating costs for

reverse osmosis are heavily dependent on inlet/outlet concentration ratio.

Capital costs for Chevron Wastewater Treatment are dependent on concentration. Operating costs for Chevron Wastewater Treatment are nearly independent of concentration.

Water Management Questions?

water management in process plants

water reuse

mprocess water flow

quality of separation

separation quality

treated water flow rate

h2s water contaminationnh3

length separator depth

water allocation problem

Documents

wte water plants

energy efï¬cient water utilization systems in process...

chilled water plants

optimization of osmotic desalination plants for water...

plants- land&water

water solutions for the manufacturing industry · 2019. 2....

chapter 2 notes -plants: provision for life- lesson 2.1...

water treatment plants process description. 2 water...

process analytical instrumentation in water treatment plants...

plants drink water

plants water&soil

water management in process plants david puckett débora...

water treatment plants

water plants

innovative fresh water production process for fossil …...

photosynthesis photosynthesis- a process by which plants...

plants need water

water tretment plants

water treatment plants - amit engineering systems3d modeling...

prsntn process plants