Evaporative Concentration of a Thermally Sensitive Chemical Chen - PowerPoint PPT Presentation

Evaporative Concentration of a Thermally Sensitive Chemical Chen 4450 Process Safety Auburn University November 27, 2006 Guest Speaker Robert D’Alessandro, P.E. Director of Process Engineering Degussa Corporation

Introduction Five Main Principles of Inherently Safer Chemical Plants: Webster: Existing in something as an inseparable element. An Integral Part Of Synonyms: Innate, native, inbred, ingrained � Substitution Use safer chemicals � Intensification or Minimization Use less hazardous chemicals � Attenuation or Moderation Use the least hazardous conditions � Limitation of Effects Use equipment fit for its service � Simplification Use less complexity Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Lecture Objectives Introduction to the following process safety related concepts: � Recognizing potential reactivity problems � Adiabatic calorimeters for obtaining proper data Reactive Example � Gassy systems versus tempered systems System Evaporative Pressure Concentration � Two-phase venting versus “all vapor” venting Relief of a Thermally � Vapor-liquid disengagement in vessels Sensitive Chemical � Integrating process safety into process design � Safety instrumented systems � Safety aspects of connected equipment Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Evaporative Concentration Steam 2,500 PPH 150 psig 10 mmHgA 83 C F 575,200 250 PPH 16.7 Btu/hr psia 70 wt% RA A-100 Z-100 P X-100 20 C From 1st Stage Three Stage Steam Concentration Jet Vacuum Process Offgas T System 15.2 C To Thermal Oxidizer RO Chilled Water 5 C 1 2 3 L 806 PPH Steam 15 C 20 60 psig mmHgA Process Condensate R-100 To Treatment 16.7 psia 1,944 PPH 70 C 308,800 T V-101 X-101 Btu/hr L 90 wt% RA Chilled Water To Crystalazer Cond. 5 C 21.7 C Note 1: Barometric Leg Note 2: Equilization Line P-100 P-101 Note 3: 3 Barometric Legs Process Flow Diagram - RA 2nd Stage Concentration Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Signs of Inherent Trouble “70 wt% RA begins, at what the chemists describe as, a slow decomposition when temperatures exceed 120 °C.” “The chemists also noted some foaming when this slow decomposition occurred.” Hints from Chemists or Operators Be suspicious of “normal” laboratory data Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Signs of Inherent Trouble MSDS – Material Safety Data Sheet: � Excellent source of general safety information � OSHA type data is good – hygiene, PPE, medical, fire fighting, etc. � Physical property data is usually good “MSDS for 70 wt% RA also indicates this temperature limit.” However, my experience indicates: � Reactivity data is lacking and sometimes wrong � Better now then in the past, but still needs improvement � Better for common petrochemicals then for specialty chemicals Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Signs of Inherent Trouble The hints from the chemists tell us that additional data is needed. What kind of data? Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Laboratory Scale Data Consider: � A typical organic fluid at 80 °C in some container � Surrounded by still air at 20 °C Laboratory Heat Loss Cooling Rate Equipment Btu / Hour / Lb °C / Minute Factor Test Tube 0.09 542 10 ml 10,840 Beaker 0.06 341 100 ml Bottom Line = Heat Loss Full Scale Cooling Rate Heat Loss Small Scale Has It Equipment Btu / Hour / Lb °C / Minute Large Scale Doesn’t Reactor 0.048 4.6 660 gallons Reactor 0.004 0.05 6600 gallons ?? WHY ?? Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Laboratory Scale Data Surface Area Surface Area to Volume Ratio Volume Volume Ratio 8.0 10 L / D = 1 10.5 124 7.0 ml L / D = 4 Surface Area / Volume (SF/Gallon) 6.0 100 4.9 57 ml 5.0 1000 4.0 0.145 2 gallons 3.0 5000 0.085 1 2.0 gallons 1.0 3.8 ml 38 ml 380 ml 3800 ml (S/V) Lab Scale >>> (S/V) Commercial Scale 0.0 0.001 0.010 0.100 1.000 10.000 100.000 1000.000 Volume (Gallons) Heat Generation ~ Volume of Contents Small Scale Experiments Must Eliminate Heat Loss Heat Loss ~ Surface Area Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Laboratory Scale Data Two Forms of Heat Loss Both are magnified by large surface to volume ratios � Heat loss to surroundings caused by temperature difference . = Δ Δ T = = If Then 0 Q UA T Q 0 � Heat loss to the sample container caused by thermal capacity of test cell. System Heat Carrying Capacity Φ ≡ Phi Factor Sample Heat Carrying Capacity + m C m C m C Decrease Test Cell Mass Φ ≡ = + f t pf t b pb b pb 1 m C m C Increase Sample Mass f t pf t f t pf t Goal for Small Commercial Vessel Phi Factor = 1.05 to 1.10 Scale Equipment Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Adiabatic Calorimeters ARC – Accelerating Rate Calorimeter � Invented by D.I. Townsend at Dow Chemical in the late 1970s Sample T � Solved the Δ T problem Heavy � But not the thermal inertia problem Wall Test Phi Factor: 2.0 ≤ Φ ≤ 4.0 Cell Containment T � Heavy wall test cell � Built to withstand internal pressure High Thermal Inertia Adiabatic Calorimeter Heating � Can not track very fast reactions Elements � Very sensitive at low reaction rates Containment Vessel � Still has important applications Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Adiabatic Calorimeters Low Thermal Inertia Adiabatic Calorimeters � Invented by DIERS in the early 1980s � Solved the Δ T problem � Solved the thermal inertia problem Phi Factor: 1.05 ≤ Φ ≤ 1.15 � Thin wall test cell � Pressure compensation prevents test cell rupture � Can track very fast reactions � Not sensitive at low reaction rates Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Adiabatic Calorimeters Containment vessel isolation ball valve Low Thermal Inertia Adiabatic Calorimeters Containment Vessel Pressure Transducer Rupture Disk (1900 psig) Auxiliary Fill Line Test Cell Pressure Transducer 3-Way Valve “Super” Filling Test Cell Magnetic Stirrer or Pressure Equalization Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Adiabatic Calorimeters Low Thermal Inertia Adiabatic Calorimeters Thin Walled Low Insulation for Maintaining Thermal Inertia Test Cell Adiabatic Conditions Pressure Containment A View of the Inside Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Evaporative Concentration The type of data that is needed is now known! Data from a Low Thermal Inertia Adiabatic Calorimeters The experiment must now be specified. Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Tempered Versus Gassy Systems Tempered Liquid Phase Systems: � T & P related directly to each other via the vapor pressure of components In Open Systems: � Heat generation or addition causes vaporization of components � Vaporization provides liquid phase cooling � When vapor removal is sufficient, T (and P) stops increasing In Closed Systems: � Essentially no vaporization occurs � Pressure increases in step with increasing temperature Examples of Tempered Systems: � Styrene polymerization � Methanol vessel under fire � Blowdown of a vessel containing liquid propane Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Tempered Versus Gassy Systems Gassy Liquid Phase Systems: � Non-condensable gases are present or formed by reaction � T & P are not simply related by the vapor pressure of the components In Open Systems: � Heat generation or addition does not cause vaporization � Cooling effects from vaporization do not occur � Instead, the sensible heat content (temperature) of the liquid increases In Closed Systems: � Pressure increases almost without bounds Examples of Gassy Systems: � Decomposition of some organic peroxides Rossonic Acid Decomposition � Decomposition of some polymers � Blow-down of a subcooled liquid containing dissolved gas Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Experimental Specification Testing 90 wt% RA in a Low Thermal Inertia Adiabatic Calorimeter: � Stainless Steel Open Test Cell � Containment Backpressure = 300 psig � Charge = 90 g (Fill ~ 75%) (Phi Factor ~ 1.1) � Hold at 70 °C Test Normal Operating Condition � Heat (4 °C Increments) and Search (5 minute holds) Until self-heating is observed � Convert to adiabatic mode � Allow test cell to self cool Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.

Adiabatic Calorimeter Data Temperature Versus Time 250 225 ∆ T ~ 120 °C 200 Temperature (C) 175 150 Heat & Search Self-Heating Detected 125 100 Adiabatic Operation 75 Normal Operating Condition 50 0 2000 4000 6000 8000 10000 12000 14000 Time (seconds) Auburn University Chen 4450 Process Safety Robert D‘Alessandro, P.E.