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Chapter 2Chapter 2

General Design Consideration

Chapter OverviewChapter Overviewthe overall economic picture generally dictates whether the overall economic picture generally dictates whether the proposed facility will receive management approval. the proposed facility will receive management approval. However, before proceeding with the development of a However, before proceeding with the development of a process design and its associated economics, process design and its associated economics, it is useful it is useful to provide an overall view of other key aspects that are to provide an overall view of other key aspects that are involved in a complete process or plant designinvolved in a complete process or plant design. In this . In this discussion, particular emphasis will be placed on discussion, particular emphasis will be placed on important health, safety, loss prevention, and important health, safety, loss prevention, and environmental considerations. Other aspects that will be environmental considerations. Other aspects that will be discussed briefly include plant location, plant layout, discussed briefly include plant location, plant layout, plant operation and control, utility use, structural design, plant operation and control, utility use, structural design, materials handling and storage, and patent materials handling and storage, and patent considerations.considerations.

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With respect to safety, health, and environmental With respect to safety, health, and environmental concerns, concerns, it is rather difficult to provide detailed it is rather difficult to provide detailed descriptions of the applicable regulations and codes descriptions of the applicable regulations and codes since these are periodically revised or updatedsince these are periodically revised or updated. . Consequently, this chapter addresses the types of Consequently, this chapter addresses the types of regulations that are relevant to chemical process and regulations that are relevant to chemical process and plant design and provides guidance where to obtain plant design and provides guidance where to obtain information on current and proposed regulations. The information on current and proposed regulations. The major emphasis, therefore, will be on general concepts major emphasis, therefore, will be on general concepts and strategies of risk assessment and reduction that are and strategies of risk assessment and reduction that are incorporated in those regulations.incorporated in those regulations.

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Health and safety hazards Health and safety hazards ShortShort--term effect term effect -- (Safety Hazard) (Safety Hazard) LD50 (Lethal Dose ) LD50 (Lethal Dose ) LongLong--term effect term effect –– (industrial health)(industrial health)TLV (threshold limit value)TLV (threshold limit value)

OSHA (OSHA (Occupational Safety and Health AgencyOccupational Safety and Health Agency))ACGIH (ACGIH (American Conference of American Conference of GovermentalGovermental Industrial Industrial HygenistsHygenists ))AIHA (AIHA (American Industrial Hygiene AssociationAmerican Industrial Hygiene Association))NIOSH (NIOSH (National Institute for Occupational Safety and HealthNational Institute for Occupational Safety and Health ))

HSE (HSE (Heath and Safety ExecutiveHeath and Safety Executive) ) EPA (EPA (Environmental Protection AgencyEnvironmental Protection Agency)), , ……

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Environmental Issues 1:2

Handling of toxic wastesHandling of toxic wastes97% of hazardous waste generation by the chemicals and nuclear 97% of hazardous waste generation by the chemicals and nuclear industry is wastewater (1988 data).industry is wastewater (1988 data).In process design, it is essential that facilities be included tIn process design, it is essential that facilities be included to o remove pollutants from wasteremove pollutants from waste--water streams.water streams.

Reaction pathways to reduce byReaction pathways to reduce by--product toxicityproduct toxicityAs the reaction operations are determined, the toxicity of all oAs the reaction operations are determined, the toxicity of all of the f the chemicals, especially those recovered as byproducts, needs to bechemicals, especially those recovered as byproducts, needs to beevaluated. evaluated. Pathways involving large quantities of toxic chemicals should bePathways involving large quantities of toxic chemicals should bereplaced by alternatives, except under unusual circumstances.replaced by alternatives, except under unusual circumstances.

Reducing and reusing wastesReducing and reusing wastesEnvironmental concerns place even greater emphasis on recycling,Environmental concerns place even greater emphasis on recycling,not only for not only for unreactedunreacted chemicals, but for product and bychemicals, but for product and by--product product chemicals, as well. (i.e., production of segregated wastes chemicals, as well. (i.e., production of segregated wastes -- e.g., e.g., production of composite materials and polymers). production of composite materials and polymers).

Environmental Issues 2:2

Avoiding nonAvoiding non--routine eventsroutine eventsReduce the likelihood of accidents and spills through the reductReduce the likelihood of accidents and spills through the reduction ion of transient phenomena, relying on operation at the nominal of transient phenomena, relying on operation at the nominal steadysteady--state, with reliable controllers and faultstate, with reliable controllers and fault--detection systems. detection systems.

Design objectives, constraints and optimizationDesign objectives, constraints and optimizationEnvironmental goals often not well defined because economic Environmental goals often not well defined because economic objective functions involve profitability measures, whereas the objective functions involve profitability measures, whereas the value of reduced pollution is often not easily quantified value of reduced pollution is often not easily quantified economically. economically. Solutions: mixed objective function (Solutions: mixed objective function (““price of reduced pollutionprice of reduced pollution””), ), or express environmental goal as or express environmental goal as ““softsoft”” or or ““hardhard”” constraints.constraints.Environmental regulations = constraintsEnvironmental regulations = constraints

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Source of ExposureSource of Exposure

Fugitive EmissionFugitive EmissionProcess OperationProcess OperationMaterial HandlingMaterial HandlingMaintenanceMaintenanceWaste Handling Waste Handling

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Exposure EvaluationExposure Evaluation

feedstock feedstock –– productproductIntermediate Intermediate –– ByBy product product –– wastewaste

::مشكالت ارزيابي مشكالت ارزيابي منابع مختلف منابع مختلف غلظت پايينغلظت پايين

متغير بودن با زمان متغير بودن با زمان

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General Control principlesGeneral Control principles

Source ControlSource ControlTransmission BarriersTransmission BarriersPersonal ProtectionPersonal Protection

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Personal ProtectionPersonal Protection

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Fire and Explosion HazardFire and Explosion Hazard

LFL & UFL (lower & upper LFL & UFL (lower & upper flammable limit)flammable limit)Classification of Fire : Classification of Fire : A,B,C,DA,B,C,DFire Protection Systems :Fire Protection Systems :Active & PassiveActive & Passive

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Safety Issues

Compound LFL (%) UFL (%) Acetylene 2.5 100

Cyclohexane 1.3 8 Ethylene 2.7 36 Gasoline 1.4 7.6

Hydrogen 4.0 75

Flammability Limits of Liquids and Gases LFL and UFL (vol %) in Air at 25 oC and 1 Atm

These limits can be extended for mixtures, and for These limits can be extended for mixtures, and for elevated temperatures and pressures. elevated temperatures and pressures.

With this kind of information, the process designer makes With this kind of information, the process designer makes sure that flammable mixtures do not exist in the process sure that flammable mixtures do not exist in the process during startup, steadyduring startup, steady--state operation, or shutstate operation, or shut--down.down.

For Gas MixturesFor Gas Mixtures

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Active Fire Protection SystemsActive Fire Protection Systems

Passive Fire Protection SystemsPassive Fire Protection Systems

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Dust and Mist FireDust and Mist Fire

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Design for Safety

Techniques to Prevent Fires and ExplosionsTechniques to Prevent Fires and ExplosionsInertingInerting -- addition of inert addition of inert dilutantdilutant to reduce the fuel concentration to reduce the fuel concentration below the LFLbelow the LFLInstallation of grounding devices and antiInstallation of grounding devices and anti--static devices to avoid static devices to avoid the buildup of static electricitythe buildup of static electricityUse of explosion proof equipmentUse of explosion proof equipmentEnsure ventilation Ensure ventilation -- install sprinkler systemsinstall sprinkler systems

Relief DevicesRelief DevicesHazard Identification and Risk AssessmentHazard Identification and Risk Assessment

The plant is scrutinized to identify sources of accidents or hazThe plant is scrutinized to identify sources of accidents or hazards.ards.Hazard and Operability (HAZOP) study is carried out, in which alHazard and Operability (HAZOP) study is carried out, in which all of l of the possible paths to an accident are identified.the possible paths to an accident are identified.When sufficient probability data are available, a fault tree is When sufficient probability data are available, a fault tree is created and the probability of the occurrence for each potentialcreated and the probability of the occurrence for each potentialaccident computed.accident computed.

Personal safetyPersonal safetySafety RegulationSafety RegulationLoss PreventionLoss PreventionHAZOP studyHAZOP studyFault tree AnalysisFault tree Analysis

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Personal safetyPersonal safety

HAZARD AND OPERABILITY HAZARD AND OPERABILITY STUDY (HAZOP)STUDY (HAZOP)

دستگاه دستگاه روشي براي معرفي تمام خطرات موجود در واحد صنعتي و يا مربوط به يك روشي براي معرفي تمام خطرات موجود در واحد صنعتي و يا مربوط به يك در اين روش هر بخش بررسي و تمام انحراف هاي در اين روش هر بخش بررسي و تمام انحراف هاي . . و مشكالت عملياتي آنها مي باشدو مشكالت عملياتي آنها مي باشد

آيند آيند ممكن از وضعيت عادي معرفي مي گردند، سپس تاثير اين انحراف ها بر فرممكن از وضعيت عادي معرفي مي گردند، سپس تاثير اين انحراف ها بر فر..بررسي و معيار اصالح آنها بيان مي شودبررسي و معيار اصالح آنها بيان مي شود

HAZOP:HAZOP: Hazard and Operability study Hazard and Operability study -- the process of the process of assessing hazards and developing control measures to assessing hazards and developing control measures to prevent accidents involving toxic, flammable or explosive prevent accidents involving toxic, flammable or explosive materials to facilitate safe operation of major hazard materials to facilitate safe operation of major hazard installations. It takes a representation of a system and installations. It takes a representation of a system and analyses how its operation may lead to an unsafe analyses how its operation may lead to an unsafe deviation from the intent of the system.deviation from the intent of the system.

Key Point: Key Point: The results of the preliminary hazard The results of the preliminary hazard analysis are fully examined in the Hazard and analysis are fully examined in the Hazard and Operability (HAZOP) study to identify and Operability (HAZOP) study to identify and understand all serious hazards.understand all serious hazards.

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HAZOP exampleHAZOP example

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HAZOPS analysis

Natural Gas fired heating system.

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FAULT TREE ANALYSIS (FTA)FAULT TREE ANALYSIS (FTA)

براي تخمين احتمال وقوع حادثه براي تخمين احتمال وقوع حادثه FTAFTA از آناليز از آناليز HAZOPHAZOPپس از معرفي و شناخت حوادث توسط پس از معرفي و شناخت حوادث توسط ..با تقسيم بندي آن به تمام اجزاء الزم براي وقوع آن استفاده مي شودبا تقسيم بندي آن به تمام اجزاء الزم براي وقوع آن استفاده مي شود

ETA:ETA: Event/Fault tree analysis Event/Fault tree analysis -- consists of an analysis of possible consists of an analysis of possible causes starting at a system level and working down through the causes starting at a system level and working down through the system, subsystem, sub--system, equipment and component, identifying all system, equipment and component, identifying all possible causes. (possible causes. (What faults might we expect? How may they be What faults might we expect? How may they be arrived at?)arrived at?)

Key Point: Key Point: Fault Tree Analysis is a logical method of Fault Tree Analysis is a logical method of analysing how and why a disaster could occur. It is a great analysing how and why a disaster could occur. It is a great technique for working out the overall probability of a technique for working out the overall probability of a catastrophic event occurring, such as a meltcatastrophic event occurring, such as a melt--down in a down in a nuclear power plant where the substantial cost involved is nuclear power plant where the substantial cost involved is obviously necessary.obviously necessary.

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با كمترين با كمترين در فاز طراحي مقدماتي ، بسياري از خطرات نهفته را مي توان شناخت و در فاز طراحي مقدماتي ، بسياري از خطرات نهفته را مي توان شناخت و ..هزينه اصالح نمود هزينه اصالح نمود

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Environmental ProtectionEnvironmental Protection

Environmental RegulationEnvironmental Regulation..اعمال نمايداعمال نمايدمهندس طراح بايد از قوانين زيست محيطي جديد اطالع داشته و درطراحي مهندس طراح بايد از قوانين زيست محيطي جديد اطالع داشته و درطراحي

Pollution Control SystemPollution Control Systemتعيين منشاء آلودگيتعيين منشاء آلودگي--تعيين خواص آلودگيتعيين خواص آلودگي--طراحي سيستم جمع آوري و انتقال طراحي سيستم جمع آوري و انتقال --انتخاب سيستم كنترلي مناسبانتخاب سيستم كنترلي مناسب--

Air pollution Air pollution AbatmentAbatment ::-- particle Removalparticle Removal-- Noxious Gas RemovalNoxious Gas Removal

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Water pollution Water pollution AbatmentAbatment

Physical TreatmentPhysical TreatmentChemical TreatmentChemical TreatmentBiological TreatmentBiological Treatment

Solid Waste DisposalSolid Waste DisposalRecycling and Chemical conversionRecycling and Chemical conversionIncinerationIncinerationPyrolysisPyrolysisLandfillLandfill

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Installed cost of wastewater-treatment plantsAppendix B (Fig B-8 & Fig B-9 )

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Thermal Pollution ControlThermal Pollution Control

Cooling Tower and Cooling PondCooling Tower and Cooling Pond

With industrial cooling towers, cooling to 90% of the ambient aiWith industrial cooling towers, cooling to 90% of the ambient air r saturation level is possible.saturation level is possible.Water circulation rates are generally 2Water circulation rates are generally 2--4 GPM/sq. ft (814 GPM/sq. ft (81--162 L/min 162 L/min m2) and air velocities are usually 5m2) and air velocities are usually 5--7 ft/s 7 ft/s (1.5(1.5--2.0 2.0 m/sm/s))Countercurrent induced draft towers are the most common.Countercurrent induced draft towers are the most common. These These towers are capable of cooling to within 2 towers are capable of cooling to within 2 °°F F (1.1 (1.1 °°C) of the wet bulb temperature.C) of the wet bulb temperature. A 5A 5--10 10 °°F (2.8F (2.8--5.5 5.5 °°C) C) approach is more common.approach is more common.Evaporation losses are about 1% by mass of the circulation rate Evaporation losses are about 1% by mass of the circulation rate for for every 10 every 10 °°F (5.5 F (5.5 °°C) of cooling.C) of cooling. Drift losses are around 0.25% of Drift losses are around 0.25% of the circulation rate.the circulation rate. A A blowdownblowdown of about 3% of the circulation rate of about 3% of the circulation rate is needed to prevent salt and chemical treatment buildup.is needed to prevent salt and chemical treatment buildup.

Purchased cost of cooling towers.Appendix B (Fig B-6)

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Noise ControlNoise Control

Plant LocationPlant LocationRaw material availabilityRaw material availabilityMarketsMarketsEnergy availabilityEnergy availabilityClimateClimateTransportation facilityTransportation facilityWater supplyWater supplyWaste disposalWaste disposalLabor supplyLabor supplyTaxation and legal restrictionTaxation and legal restrictionSite characteristicsSite characteristicsFlood and fire protectionFlood and fire protectionCommunityCommunity factorsfactors

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Transportation facilityTransportation facility

Back

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Back

Back

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Plant LayoutPlant Layout

Plant Operation and ControlPlant Operation and Control

InstrumentationInstrumentationMaintenanceMaintenanceUtilities Utilities Structural design Structural design Storage and Building Storage and Building Materials Handling Materials Handling

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InstrumentationInstrumentation

اندازه گيري كننده اندازه گيري كننده نشان دهندهنشان دهندهثبت كننده ثبت كننده

كنترل كننده كنترل كننده اعالم خطراعالم خطر

For Extra informationFor Extra information : :

Fig BFig B--10 :10 :Purchased cost of liquid-level gages, flat-glass typeFig BFig B--11 :11 : Purchased cost of level controllersFig BFig B--12 :12 : Purchased cost of flow indicatorsFig BFig B--13 :13 : Purchased cost of temperature recorders and indicatorsFig BFig B--14 :14 : Purchased cost of pressure indicators

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MaintenanceMaintenanceUtilitiesUtilities

Table BTable B--1 & Table 61 & Table 6--1414

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Structural designStructural design

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StorageStorage

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Drum Type VesselsDrum Type Vessels

Liquid drums are usually horizontal. Gas/Liquid Liquid drums are usually horizontal. Gas/Liquid separators are usually verticalseparators are usually verticalOptimum Length/Diameter ratio is usually 3, range is 2.5 Optimum Length/Diameter ratio is usually 3, range is 2.5 to 5to 5Holdup time is 5 minutes for half full reflux drums and Holdup time is 5 minutes for half full reflux drums and gas/liquid separators gas/liquid separators Design for a 5Design for a 5--10 minute holdup 10 minute holdup for drums feeding another columnfor drums feeding another columnFor drums feeding a furnace, a holdup of 30 minutes is a For drums feeding a furnace, a holdup of 30 minutes is a good estimategood estimateKnockout drum in front of compressors should be Knockout drum in front of compressors should be designed for a holdup ofdesigned for a holdup of 10 times the liquid volume 10 times the liquid volume passing per minute.passing per minute.

Pressure VesselsPressure VesselsDesign Temperatures between Design Temperatures between --30 and 345 30 and 345 °°C (C (--22 to 653 22 to 653 °°F) is F) is typically about25 typically about25 °°C (77 C (77 °°F) above maximum operating temperature, F) above maximum operating temperature, margins increase above this rangemargins increase above this rangeDesign pressure is 10% or 0.Design pressure is 10% or 0.6969 to 1.7 bar (10 to 25 psi) above the to 1.7 bar (10 to 25 psi) above the maximum operating pressure, whichever is greater. The maximum maximum operating pressure, whichever is greater. The maximum operating pressure is taken as 1.7 bar (25 psi)above the normal operating pressure is taken as 1.7 bar (25 psi)above the normal operation pressure.operation pressure.Minimum thicknesses for maintaining tank structure are:Minimum thicknesses for maintaining tank structure are:

6.4 mm (0.25 in) for 1.07 m (42 in) diameter and under6.4 mm (0.25 in) for 1.07 m (42 in) diameter and under 8.1 mm (0.32 in) for 1.078.1 mm (0.32 in) for 1.07--1.52 m (421.52 m (42--60 in) diameter60 in) diameter

9.7 mm (0.38 in) for diameters over 1.52 m (60 in)9.7 mm (0.38 in) for diameters over 1.52 m (60 in)Allowable working stresses are taken as 1/4 of the ultimate streAllowable working stresses are taken as 1/4 of the ultimate strength ngth of the materialof the materialGuidelines for corrosion allowances are as follows:Guidelines for corrosion allowances are as follows:

0.35 in (9 mm) for known corrosive fluids,0.35 in (9 mm) for known corrosive fluids,0.15 in (4 mm) for non0.15 in (4 mm) for non--corrosive fluids, corrosive fluids, 0.06 in (1.5 mm) for steam drums and air receiv0.06 in (1.5 mm) for steam drums and air receivers.ers.

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Storage VesselsStorage Vessels

For less than For less than 44 m3 (m3 (~~1000 gallons) use vertical tanks on 1000 gallons) use vertical tanks on legslegsBetween Between 44 m3 and m3 and 4040 m3 (m3 (~~1000 to 10,000 gallons) use 1000 to 10,000 gallons) use horizontal tanks on concrete supports.horizontal tanks on concrete supports.Beyond Beyond 4040 m3 (10,000 gallons) use vertical tanks on m3 (10,000 gallons) use vertical tanks on concrete concrete foundationfoundationLiquids with low vapor pressures, use tanks with floating Liquids with low vapor pressures, use tanks with floating roofs.roofs.M. Raw material feed tanks are often specified for 30 M. Raw material feed tanks are often specified for 30 days feed supplies. Storage tank capacity should be at days feed supplies. Storage tank capacity should be at 1.5 times the capacity of mobile supply vessels.1.5 times the capacity of mobile supply vessels.

( (For example, 28.4 m3 (7500 gallon) tanker truck, 130 For example, 28.4 m3 (7500 gallon) tanker truck, 130 m3 (34,500 gallon) rail carsm3 (34,500 gallon) rail cars ) )

Material HandlingMaterial Handling

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Patent ConsiderationPatent Consideration

QUESTIONS AND DISCUSSIONQUESTIONS AND DISCUSSION

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Vinyl chloride Health effectsVinyl chloride Health effects

Vinyl chloride depresses the Vinyl chloride depresses the central nervous systemcentral nervous system, and inhaling its , and inhaling its vapors produces symptoms similar to alcohol vapors produces symptoms similar to alcohol intoxicationintoxication. These . These include headache, dizziness, and loss of coordination, and in seinclude headache, dizziness, and loss of coordination, and in severe vere cases may progress to cases may progress to hallucinationhallucination, unconsciousness, and death by , unconsciousness, and death by respiratory failurerespiratory failure..In laboratory animals, exposure to vinyl chloride during In laboratory animals, exposure to vinyl chloride during pregnancypregnancyhas produced has produced miscarriagesmiscarriages and and birth defectsbirth defects. Its effect on human . Its effect on human reproduction is unknown.reproduction is unknown.LongLong--term exposure to vinyl chloride can cause chronic skin term exposure to vinyl chloride can cause chronic skin irritations and has also been linked to a painful inflammation oirritations and has also been linked to a painful inflammation of the f the extremities called extremities called Raynaud's syndromeRaynaud's syndrome. Vinyl chloride is considered . Vinyl chloride is considered to be a to be a carcinogencarcinogen and has in particular been linked to certain and has in particular been linked to certain cancerscancers of the of the liverliver——chiefly, chiefly, hepatocellular carcinomahepatocellular carcinoma