Dust Explosion Is One Of The Major Hazards Engineering Essay

Dust fusillade Is One Of The Major Hazards Engineering EssayDust salvo must(prenominal)iness be correspondled but government agency of necessary freeing atomic number 18a discipline, Vessel readiness, likewise following proper mathematical operational procedures and maintaining good housekeeping.Here a new cornerstone pickax embed and silo for charge card manufacturer is juted. So, as a safety advisor the vent coat for a silo is presented to vent a corpse enlargement.Information required for the figuring of the vent sizing are strength of the vessel i.e. silo, fit properties of the junk, size and shape of the vessel, the static activation ram that is to open the venting in font of any pinch rise, condition of the patter cloud.If the propagate is found to be toxic then venting should non be done if thithers immediate detriment to the environment. But in nigh un neutralizeable circumstances then the venting is done with an endangered area sh every last(p redicate) be specified. For that safe loose area must be calculated to vent the stud to the atmosphere.And location of venting is chosen on the top of the silo i.e. vertical venting. This assumption made on the condition that the silo is sited in a congested area. Horizontal venting go out vex harm the force play working in the whole works area.Plant SketchSilo Air to bug out filterPneumatic ConveyorCyclonePowder Inletfrom plantAir BlowerVibrating outlets to stand filling putsData devoted,Silo is of cylindrical shape.Diameter = 10m meridian = 30m beam duct length = 15 mSilo Design pressure = 0.25 bargMaterial stored in silo is plastic advocate and as well as embroils Methylene dianiline (MDA).Here the constellate is tested in and 20 litre sphere apparatus to find the easy layimum rate of pressure rise per unit cartridge clip. The main apparatus is ambit effusion vessel, propagate dispersion system, fervour source, Pressure monitoring system and control system. Thi s test done as per BS EN 14034-22006. And it is found that(dp/dt) max = 928 bar.s-1Where (dp/dt) max Maximum rate of pressure (p) rise per unit eon (t)The objectives of this design arei. To vent the deflagrating that occurs inside(a) the vesselii. To avoid the injury to personnel by vent dischargeiii. To limit the damage of the vesseliv. To limit the damage of the nearby structuresThe following steps are identify for venting sizing with reference toi. Dust deflagration index Kst must be found,Kst = (dp/dt)max * V 1/3Where (dp/dt) max Maximum rate of pressure (p) rise per unit time (t) =928 bar/sAnd volume of the test apparatus is 0.02m3Kst = 928 * (0.02)1/3 bar.m.s-1Kst = 252 bar.m.s-1ii. Now maximum effusion overpressure occurs during dust explosion in an wrap vessel (non- give vent vessel) Pmax which is to sic the explosive characteristics of the dust. Procedure for measuring Pmax is done in 5litre apparatus and the apparatus is designed to withstand an internal overpressu re of 20 bar. First required amount of dust is come ton for the test. Then the dust is dispersed in the vessel at atmospheric pressure and sooner that the initial temperature is noted down. Then initial pressure Pi i.e. just a moment before ignition is noted. And the pressure rise recorded as a function of time. And from pressure time scent Pex is determined for the particular dust concentration. And the test is done for various dust concentration and the Pex results are plotted with various dust concentration until the maximum place of Pex is found. And that maximum value is the maximum overpressure Pmax.This Pmax and Kst plays crucial component in determining the vent size and design for explosion protection. Here dust mixture establishment is not known, so the vent size is based on highest Kst and Pmax value. The result of Pmax for various dust classes is referred from BS EN 14034-22006, the put back is shown at a lower placeKst (bar.m.s-1)Dust explosion classPmax (bar)0 S t 1 9200 St 2 10Kst 300St 3 12 delay 1aWhere,St 1- moderate explosibleSt 2 strong explosibleSt 3 very strongly explosibleHence from the table higher up Pmax is taken as 10 bar for Kst = 252 bar.m.s-1 and the dust is classified as St 2.iii. Now the vessel design pressure selection must be measured, if the landmark vessel is designed as ASTM then Pmawp (Maximum allowable work pressure) backside be calculated. Here it is given that design pressure is 0.25barg.Venting provided should be sufficient to reduce the enclosure vessel rapture due to reduced maximum overpressure, Pred,maxHere Pred,max shall be chose shall not exceed two-third of the vessel strength. Venting shall be provided such that Pred,max shall not exceed the vessel strength to counteract the rapture of vessel during venting.Pred,max (Pes/ DLF)Where, DLF dynamic Load factor as a result of pressure rise. In absence of detailed structural analysis, it is take for granted that DLF = 1.5 the design based on weakest structural element.i.e. Pred,max (2/3)(Pes)WherePes enclosure strength in barHence, Pred,max = 0.166 bariv. Vessel Height to diameter ratio, the ratio of height to diameter of the vessel must be included in determining the vent area. Increase in ratio of height to diameter increases the attack propagation inside the vessel. Hence the estimation of the ratio is given down the st cinchs,Veff = r2 hWhere Veff is the volume of the cylindrical vessel were flame seat travel along the path.h Height of the cylinderr radius of the cylinderVeff = 3.14 * 5* 5* 30 = 2355m3Aeff = Veff / HWhere Aeff is the effective area of the cylindrical vesselAeff = 2355 / 30 =78.5 m2Deff = ((4*Aeff)/)1/2Where Deff is the effective diameter of the cylindrical vesselDeff=((4*78.5)/3.14)1/2 = 10mH/D = 30/10 = 3mv. Venting bury operation, the following factors to considered for the venting cover operation such as venting opening shall be free and clear, should be obstructed by weather conditions and any dust deposits. The vent cover shall open at its static activation over pressure Pstat. And vent cover should withstand the pressure within the static activation overpressure Pstat.. Here venting cover with specialised mass And Hence Pstat = 0.2 bar.Sizing of vent area, here the specific situation must be considered for the venting sizing. Here the material is transferred by pneumatic conveyor. And this is classified as Inhomogeneous dust distribution as per unexampled findings on explosion venting by R.Siwek.For vessel length L 10mA = 0.0011 * Kst* H *Df * (1/Dz) (8.6 log Pred,max 6) 5.5* log Pred,max + 3.7 ( 1 +1.715 * Pred,max -1.27 * log (H/D))Where, Df diameter of the pipeline, here its assumed as 0.1m for effective dust reductionA Vent area m2Dz effective diameter of the cylindrical vesselDz =( (4*v)/ ) 1/3 = (( 4*2355)/3.14)1/3 = 14A = 0.0011 * 252 * 30 * 0.1 * (1/14) (8.6 log 0.166 6 ) 5.5 log 0.166 + 3.7 (1 + 1.715 * 0.3 -1.27 * log 3)A = 30 m2Effect of vent ductin g, duct is normally to vent the discharge to a safe area a air from the work area. But increase in duct length will increase reduced maximum explosion pressure.P red,max = -0.03267 * l*(H/D) + 0.3481 * l0.798Where, l length of the duct (m)P red,max maximum reduced explosion pressure with vent ductP red,max = -0.03267 * 15 * (30/10) + 0.3481 * 150.798P red,max = 1.5 barP red,max = 0.2 *(C1 C2) * (1-(H/D)) + C1Where C1 = P red,max * (1 + 17.3 *(A*V-0.753)1.6 * l) = 1.027C2 = (0.0586 * l) + 1.023 * P red,max0.981 (0.01907 *l) = 0.5P red,max = 0.8 barAnd from the above equation relationship between the reduced maximum explosion pressure with vent duct and duct length can be found and also necessary increase in cylindrical vessel strength can also be estimated.Since the preparedness is still beingness designed and from the above result of with effect of vent duct it is evident that reduced maximum explosion pressure increases above the vessel design pressure. So the increase in des ign pressure and the vessel strength must be re-considered if vent duct is apply to deflagrate the flame.Safe discharge,Maximum flame length for dust,X = Q*V1/3Where Q 8 for vertical dischargeX = 8 * (2355)1/3X = 106.4 mMaximum flame width,W = 1.3 * (10*v)1/3 = 37mMaximum external pressure (dust)P = 0.2 * Pred,max * A0.1 * V0.18 = 0.188 barWhere P maximum external pressureA Vent areaV Volume of the cylindrical vessel.2.This bag filling facility handles plastics powder which generates dust must be examined for the explosive characteristics. For that we need to analyse the chemical compositions in it. The explosive dust decomposes generating large enormous energy. This decomposition includes oxygen in the molecule so it is not necessary that it needs air. So it is principal(prenominal) to screen the chemical composition first, if the test indicates the presence of explosive characteristics then necessary dust explosion prevention and protection techniques must be utilize as a basis of safety.In order to prevent the dust explosion following techniques are employi. Controlling the source of ignitionii. InertingFor explosion protecting the following techniques are usei. Explosion containmentii. Explosion suppressioniii. VentingDUST EXPLSIONPROTECTIONPREVENTIONControl of ignition containmentSource prohibitionInertingVentingNow the details of each technique are explained in detail belowControlling the source of ignition, dust explosion cannot occur unless theres a source of ignition. And hence a careful analysis must be done in design, operation and maintenance for the likely sources of ignition. Here are some of possible sources of ignitiona. hot surfaceb. sparkc. electrostatic sparkd. warmnesse. frictionf. flamesFlames are one of the sources which can easily ignite the dust. invest heating i.e. using of burners can be avoided in process where dust generation is possible. Welding works carried on the silo which has possible dust generation inside the ves sel. So all hot works carried on silo must be allowed as per the statutory requirements. Any Internal combustion engines near the silo might take in the dust generated nearby and can possess explosion. And hence this combustion engine can be avoided or use of flameproof combustion engines. electric power is also one of the sources of ignition. Electric spark which are produced from electrical equipment, if comes in contact with dust will result in explosion. Hence all the electrical equipment must be intrinsically safe and also ATEX 137 EU directive 95/9/EC certified equipment should be used depending upon the dust and zone classification. So this must be done during procurement stage. Once ATEX is employ then zone classification must be done as a part of ATEX requirement by analysing the possible generation dust from the process i.e. Zone 20 dust generation is often, zone 21 dust generation likely to occur or Zone 22 dust generation not likely to occur.Dust depositing on hot s urface will cause explosion depending on the temperature and geometry of the surface. In most of the cases this can be avoided by good housekeeping. And also Ignition occurs only when the surface temperature reaches the minimum ignition temperature of the dust.Static electricity is also one of the major hazards in process and chemical industries. When a charged particle comes in contact with the opposite or miscellaneous object there will be transfer of charge and will results in spark. Since the powder have charged particle, when it comes in contact with dissimilar particle in transferring or free falling there will be transfer of charge which will generate spark. And the spark generated can cause ignition of the dust. Hence all the metal containers must be earthed so that the charge generated will leak away to the earth. And use non conducting materials are recommended in construction. down the stairs diagram show difference between earthed and non-earthed conductorFigure 2a Ha zards in non-earthed conductorFriction is also one of the ways that dust cloud can be ignited. That is when hot particles come in contact with mechanical equipment by rubbing or jolting against the equipment can ignite the dust cloud. This friction ignition depends upon the maximum velocity of the hot particle impacting against the hot surface. And hence use of such mechanical equipment should be avoided.And the another(prenominal) possible chances of ignition of dust clouds can be through spontaneous combustion. So this type of burning occurs due to self-heating as a result of internal exothermic reaction which is followed by thermal runaway. If this heat release is unable escape will result in ignition. And also sufficient oxygen and dust concentration must be present for the thermal runaway ignition. Hence the safe way is to displace the oxygen is by inerting.Inerting is a process by sending inert unions to remove or prevent the explosive atmosphere formation. The main object ive is to eliminate or to reduce the oxygen level below the lower flammability limit in order to avoid the catastrophic dust explosion, in some case combustion can also occur in very low oxygen level so in that case is safe to replace all the air with inert gases. Even sometimes explosive dust generated inside the vessel can be diluted into non explosive dust by passing certain inert dust e.g. limestone. When inerting theres chance of inert gases gets trapped inside the vessel, where personnels are accessible for hold space works, this will result in asphyxiation. Hence proper statutory rules must be followed in entry of confined space.Care should be taken when inert gases are sent into the distribution line. That is before passing the inert gases the impurities such as hazardous content moisture etc. should be outside from the inert gases by means of filter. And flow of the inert gases must be maintained by the pressure monitoring and controlled. Flow chart for inerting process is shown belowInertingUse of inert dust as an inert mediumSuitable inert gas available e.g.) N2, co2 etcPerforming oxygen limiting bill at process temperature and pressureDesign dust inert systemEnsure the reliability of the monitoring systemInert gas cost when compared to other safety technique, are the cost found satisfactoryConsider basis of safety for design and operationAnd some the other available prevention techniques include installation of pressure sensor, alarm system in-case of overpressure, Automatic shutdown system in-cases of overpressure, Level indicator, correct operational procedures and Proper maintenance and inspection procedures.Explosion containment is used to withstand the explosion pressure rise and to prevent the rupture of the containment. The explosion containment usage is accepted when the release of the process materials is not acceptable. First maximum explosion pressure Pmax must be determined, since it is the crucial factor in explosion containment. H ence pressure resistant vessels are designed to withstand the maximum explosion pressure without any deformation or rupturing the vessel. And hence the distort induced by the maximum explosion overpressure should not exceed 50% of the yield strength of the weakest part.Explosion pressure shock resistant vessel is also designed to handle the maximum explosion pressure but deformation occurs to some extent. And the stress induced by the maximum explosion overpressure should not exceed 90% of the yield strength of the weakest part. Logical flow chart for explosion containment is shown belowExplosion ContainmentMulti-volumeSingle volumeCan explosion be contained by knowing Pmax and plant design?Are the multiple volume is mechanically isolatedIs exaltation of vessel acceptable?Use pressure shock resistant vesselUse pressure resistant vesselConsider basis of safety for design and operationCost valid when compared to other safety techniquesSuppression is a technique which identifies the starting point of explosion and extinguishes the growing sex. Normally suppressor is used whenever it is difficult to discharge the pressure and flame in a safe area. Normally it takes 40 90ms for an explosion to occur when the dust gets ignited. So now the explosion detector detects the pressure rise in the vessel and it is designed to set the alarm when it reaches the reference pressure rise and activates the suppressor so that it suppresses/extinguishes the growing fire ball inside the vessel. Suppressor can also be used in parallel with venting where sufficient venting area is not achieved. And also it is to noted that explosion detector should withstand to the vibration, shock and resistant against corrosion. Below figure shown is the normal working of suppressor in the vessel.Normally suppression can be used for a vessel volume up-to 1000m3. For vessel larger than 1000m3 explosion suppression can be used and the explosion suppressor must be within the vessel volume boundary .Fig 2b Suppressor workingIf a vessel is without suppressor and dust explosion occurs in a enclosed vessel then the pressure rise grow and attains destructible level which is shown below in chart (line A). If a suppressor is installed and suppressor extinguished before the explosion then the maximum pressure rise will be reduced Pred within the maximum vessel design pressure, shown below in graph (line B). In order to achieve the above it also depends upon the suppressor location, suppressor discharge rate and also number of suppressor placed in the vessel. chart 2a Pressure rise with suppressor and without suppressorThere are many types of suppressors available such as hemispherical suppressor, High rate discharge suppressor are used. Normally high rate discharge are most widely used because for their high discharge rate to suppress the fire. In hemispherical suppressor usually liquids i.e. water is used as appetite suppressant and can store upto 5 litres. And the initial velocity of hemispherical suppressor is 200m.s-1 and the discharge time is 10 30 ms. For high rate discharge suppressor the suppressant used can be liquid or dry powder. It can suppressant discharge time is within 10 millisecond and suppressant stored upto 40kg.And the suppressant materials used in order to supress the fire must quench the combustion. And some of the unremarkably used suppressants are dry powder i.e. dry chemical and water.Flameless venting is done to vent the explosions without any put on the line of external flame. Flameless venting device consists of flame arrestor which quenches the flame that propagates outside from the vessel. The main principle is that the arrestor reduces the fuel from flame below the ignition temperature by energy dissipation in the flame arrestor.3.Here in this bag filling facility, use of hazardous substance involved. Hence this operation must abide to control of substance hazardous to health Regulation 2002 (As Amended) (COSHH) to control the hazards to the human health.Here in this bag filling facility there is use of plastic powder which get filled and packed. In this plastic power has an additive known as Methylene dianiline. This plastic powder is a thermoplastic intended for use in injection of moulding machine.This methylene dianiline is a carcinogen which causes cancer when it is inhaled by the people intermeshed in bag filling operation. So it is necessary to conduct control of substance hazardous to health risk assessment. And to evaluate the allowable exposure limits and the necessary measure to be taken while handing the hazardous materials.Main steps to be followed to prevent the health hazards and to be with COSHH are as followsi. Determine the riskii. Control measure implementationiii. Control the exposureiv. Continual improvement and practice of the control measure implementedv. Monitoring the exposure level with the control measuresvi. Providing health monitoring check upvii. Prepare Emergency plan and conduct emergency mock praxisviii. Providing training and necessary information to the employeesSubstances or chemicals that are hazardous to personnel health will come under COSHH. Here methylene dianiline is used which is set as a potential drop carcinogen and hence the operation should comply with COSHH to control the health hazards and improve the operation.Determine the hazardThe first step is to identify the hazard whether the substance used in the process causes health hazard to employee engaged in work. Here it is identified that Methylene Dianiline is a potential carcinogen. So operators engaged for bag filling, sealing and engaged in cleaning activities are at risk if exposed. So first we need to find the possible exposure points. From analysing the operation involved in bag filling facility. The possible release/exposure points are identified below,i. filling arms in bag filling station building it vibrates to prevent cloggingii. Opening the valve fast will cause sud den release of pressure.iii. Bag sealing possible dust generation since the bag is left openediv. Cleaning the spilled dust near filling areav. Pneumatic conveyor possible leak point will cause dust dischargeHere it is identified that possibility of the substance route to affect operator health is through inhalation when released in air.And hazards of methylene dianiline and its chemical properties are taken from knap classification, Now CHIP regulation gradually replaced by European CLP. And the hazard classification is taken from European regulation EC No 1271/2008 on Classification labelling and Packing (CLP) from tabularize 3.2 part3 of Annexure I to directive 67/548/EECIndex No foreign Chemical IdentificationEc NoCAS noClassificationLabellingConcentration Limit612-051-00-14,4Methylenedianiline202-974-4101-77-9Crac Cat 2R 45 Mutta.Cat,3 R 68T R39/23/24/25Xn R48/20/21/22R43N R51-53TNR45-39/23/24/25-43-48/20/21/22-68-51/53S53-45-61Table 3aClassification is taken from European regulation EC No 1271/2008 on Classification labelling and Packing (CLP) from Table 3.1 part3 of Annexure VI to directive 67/548/EECIndex NoInternational Chemical IdentificationEC NoCAS noClassificationLabelling dubious Class and Category codesHazardous Statement CodesPictogram signal word codeHazardous Statement CodesSuppl. Hazardous Statement Codes612-051-00-14,4Methylenedianiline202-974-4101-77-9Carc 1BMuta 2STOT SE 1STOT RE 2Skin sens 1AquaticChronic 2H350H341H370**H373**H317H411GHS08GHS07GHS09DgrH350H341H370**H373**H317H411Table 3bWhere R Risk phase and H Hazard , Classification of levels of danger i.e. harmful, toxic, very toxic as per CHIP regulation. Here MDA is classified as potential carcinogen R 45 Cancer causing substance.Deciding proper safe guarding measureSince here the plant is in designing stage so the possible release/exposure points, population exposed to the hazardous substance and route of entry are identified and necessary control measure are indentified bel ow to implement from the designing stage. So COSHH essential uses out of the risk assessment information it chooses one of the methods for control measure shown below,Figure 3aThe factors used in identifying assume controls measure are in below figure,Figure 3bSo the following steps are followed in identifying adequate control measure as mentioned in COSHH essentials Easy steps to control chemicalsi. Group the hazards identifiedii. Grouping the physical properties of the amount usediii. Asses the anticipated exposureiv. Now combine step 1 to 3 to form a generic assessmentGrouping the hazard, hazards are classified between A to E by R-Phase given in CHIP and H-Phase given in CLP. Below the table shows the classification of hazard group. In the below table units, mg/m3 milligrams per cubic meter and ppm parts per million. From below table methylene dialine classified under group E dust.Table 3cNow to determine the predictive exposure we must first classify the hazardous substance p hysical properties. Here in bag filling operation, hazardous substance is in dust form, since the plastic powders are granule will generate dust. So as per COSHH essential they have presented a table for identifying the determining factors of the hazardous substance. That is the factor for deciding the physical properties for solid are dustiness and for the liquid is the volatility.And based upon the below shown table here methylene dianiline is identified as fine solid and light power and the corresponding determinant is identified as high.Table 3dAnd after identifying the determinant and amount used as per COSHH essential has identified four band of exposure potential and the table is shown below,Table 3eHere in bag filling and packing operation the main product is plastic powder which contains methylene dianiline as an additive. So the quantities used which assumed to be in tonnes, the main aim of this plant is packing plastic powder. And the exposure predictor band here it is i dentified as EP 4.sNow to decide which the control approach is adequate luxuriant to control the situation of health hazard has to be identified from the range given which is used in COSHH essential. And table is shown belowTable 3fAnd based upon the above control approval table and exposure predictor table COSHH essential formed a table relating exposure predictor to control approach. And the table is shown below.Table 3gIn-order to choose the type of control measure recommended we have to relate the target airborne exposure to the exposure predictor band .Hence for this bag filling facility type-4 control is recommended because the concentration level of the dust is unknown.Sample COSHH Risk assessmentStep 1Step 2Step 3Step 4What are the hazardWhat will harm and who?What are you doingImprovements neededWhoWhenCheckBreathing in dust from filling stationSince the dust contains MDA might cause cancer and irritates the respiratory systemDust maskGet cab and filtered air supplyConveyo r to silo, to filling stationNobodyDust parentageCheck for leaks weeklyBagging plastic powderCharge handedStorage and dispatchForklift driverDust maskGet cab and filtered air supplyCleaning the plastic powder dust spillCharge handBrushingVacuum hose to dust extractionChanging dust filterCharge handUse of P3 respiratorContract out this workAlsoAction TakenAction neededExamination screen out COSHHSupervisionInstruction and trainingEmergency PlanHealth SurveillanceMonitoringReview DateRecommendationsHere to reduce the possible exposures to hazardous substance below are the following recommendations,i. Minimizing the generation of plastic dust such as designing conveying system in such a way to reduce the impact with hard surface to reduce the dust generation i.e. use of long sweep elbows.ii. Minimising the release of plastic dust such as keep silo in good conditions i.e. avoid crack, proper maintenance etc., maintain the transfer equipment in good seal condition to avoid leaks.iii. Plastic dust can be captured and contained.iv. Create awareness among the employee about the hazards associated in handling hazardous substance and use of MSDS.v. Regular health surveillance must be conducted to employee exposed to risk.vi. Use of proper respiratory PPEs while handling with plastic powder. As per COSHH essential it is identified suitable PPEs for the selected group hazard. Table is shown below and it is identified as Assigned protection factor 200. This APF is in reference with BS 4275Table 3h4.Project DescriptionThe new bag filling line and silo is being constructed for a plastic manufacturer which is located in congested area which means the silo is located in between the nearby structures and objects but the whole plant is located in plain and partly terrain area. This facility involves transfer of plastic powder from the plant to silo for storage so that it can used to store plastic powder prior to the bagging and distribution. Here in the silo there is possibl e release of dust into the atmosphere due to overpressure or overfilling. Since the dust generated inside the silo is vented to atmosphere so it must meet to the current environment legislation in order to avoid air pollution. From Silo the plastic powder is sent to bag filling station. The bag filling station comprises a building in which there are four bag filling stations. Hence an environmental impact aspect must be undertaken before the commencement stage .Plant SketchSilo Air to bag f