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1David Sediqi, Kori Mondin, Faisal Najem, Sharath Reddy, Jerrell Ross Team 10 FlammabilityDavid Sediqi, Kori Mondin, Faisal Najem, Sharath Reddy, Jerrell Ross
2IntroductionMost chemical plants contain flammable materials and face hazards related to their combustionThe majority of the worst chemical plant accidents involved flammable materials.To avoid and manage these risks, 3 important concepts must be recognized and understood:The Anatomy of the fireThe Characteristic Properties of flammable materialsProcedures used to reduce fire and explosion hazards
3Minimize the Risks of Flammable Materials Nearly all of the WORST chemical plant accidents involved flammable materials.Flammable materials can cause severe damage in the form of fires and explosions if not handled properly.The video to the left, shows a Texas Fertilizer plant explosion last year.Over 100 people injured.
4Anatomy of Fire/Explosion A fire can only occur when a fuel, oxidant, and an ignition source is available .Fuel- the concentration must be present at a certain relative amount to the oxidant. Example: Gasoline, ethanol, methane, ethane, etc.Oxidant- the concentration must be present at a certain relative amount to the fuel. Example: Most common one O2 , but can include Cl2, and nitratesIgnition Source- can range from a spark to a flame, but must be strong enough to start a fire.Fires occur over a long time frame and have a low energy release rate, while explosions are the opposite in both ways.
5Properties of Flammable Materials Flammable gases and liquids can be characterized by properties that are determined experimentally.Properties include :Flammability LimitsLimiting oxygen concentrationMinimum ignition EnergyAutoignition TemperatureFlash PointCrowl D A. Minimize the risks of flammable materials. Chemical engineering progress 2012;108(4):28-33.
6Flammability LimitsFlammable gases and liquids can be characterized by properties that are determined experimentally.One of the main characteristics is Flammability limits. This is divided in two subcategories: Lower flammability limit (LFL) and Upper Flammability limit (UFL)LFL- the concentration of fuel vapor in which below it, no explosion will occur. The mixture is too dilute .UFL- the concentration of fuel vapor in air in which above it, no explosion will occur. The mixture is said to be too concentrated or rich.The LFL and UFL are determined experimentally by mixing flammable gas and an oxidant in a closed container. If ignition occurs, the pressure increase to a maximum.Lower Flammability Test appartus MSB International Fire Behaviour and Fire Suppression Course 2011
7Matlab Max Pressure vs Fuel Concentration c = linspace(0,10)dd=polyfit(C,E,2)%take polyfit values to generate equation of parabola belowy= *c.^ *c ;plot(c,y)hold on;scatter (C,E)hold offaxis([ ])title('Max. Explosion Pressure Vs. Fuel Concentration in Air')ylabel('Maximum Explosion Pressure (barg)')xlabel('Fuel Concentration in Air (vol%)')
8Temperature Effects on Flammability Limits Temperature has a large effect on flammability limits of species. The equations below show this relationship between flammability limits and temperature.Calculation of Flash Points and Flammability Limits of Substances and MixturesCalculation of Flash Points and Flammability Limits of Substances and Mixtures
9Matlab Determination of Lower Flammability Limits function [ ] = FL( T,Hc,LFL25 )%calculates the lower flammability limit of a substance at a given temperatureif nargin<3, error('Temperature, Hc and Lower Flammability Limit Required')end%diplays an error if the required information is not givenLFLi=LFL *(T-25)/Hc;%equation used to calcuate LFL using LFL at 25 degrees celsius, the given%temperature and the enthalpyfprintf('LFL= %8.2f\n',LFLi);%displays the LFL
10Matlab Determination of Lower Flammability Limits function [ ] = UFL( T,Hc,UFL25 )%calculates the Upper flammability limit of a substance at a given temperatureif nargin<3, error('Temperature, Hc and Upper Flammability Limit Required')end%diplays an error if the required information is not givenUFLi=UFL *(T-25)/Hc;%equation used to calcuate UFL using UFL at 25 degrees celsius, the given%temperature and the enthalpyfprintf('UFL= %8.2f\n',UFLi);%displays the UFL
11Flammability Limits of Mixtures The flammability limits of mixtures can be calculated by the equations to the right. These equations incorporate the flammability limits and mole fractions of the species that make up the mixture.Crowl D A. Minimize the risks of flammable materials. Chemical engineering progress 2012;108(4):28-33.web.mst.edu/~dludlow/classes/che258/Flammability.ppt
12Matlab Determination of Lower Flammability Limits for Mixtures function [ ] = LFLmix()%calculates lower flammability limit for a mixtureyi=input('input y in matrix form (ex. [y1 y2 y3])for each flammable species in the mixture\n');%receives input values for composition of mixtureLFLi=input('input LFL in matrix form (ex. [LFL1 LFL2 LFL3])for each flammable species in the mixture\n');%receives input values for LFL of each species in mixturedivide=yi./LFLi;%divides each composition by the flammabilitysum=0;%sets sum equal to 0[m,n]=size(divide);%sets m equal to number of rows%sets n equal to number of columnsfor i=1:nsum=sum+divide(m,i);%adds up all yi/LFLiendLFLmix=1/sum;%calculates LFLmixfprintf('LFLmix= %8.2f\n', LFLmix);%prints value of LFLmix
13Matlab Determination of Upper Flammability Limits for Mixtures function [ ] = UFLmix()%calculates lower flammability limit for a mixtureyi=input('input y in matrix form (ex. [y1 y2 y3])for each flammable species in the mixture\n');%receives input values for composition of mixtureUFLi=input('input UFL in matrix form (ex. [UFL1 UFL2 UFL3])for each flammable species in the mixture\n');%receives input values for LFL of each species in mixturedivide=yi./UFLi;%divides each composistion by the flammabilitysum=0;%sets sum equal to 0[m,n]=size(divide);%sets m equal to number of rows%sets n equal to number of columnsfor i=1:nsum=sum+divide(m,i);%adds up all yi/LFLiendUFLmix=1/sum;%calculates LFLmixfprintf('UFLmix= %8.2f\n', UFLmix);%prints value of LFLmix
14Matlab Examples for Flammability Limit Calculations >> LFLmix()input y in matrix form (ex. [y1 y2 y3])for each flammable species in the mixture[.5 .5]input LFL in matrix form (ex. [LFL1 LFL2 LFL3])for each flammable species in the mixture[5 3]LFLmix=>> FL(100,889,5)LFL=>> UFL(100,889,15)UFL=>> UFLmix()input y in matrix form (ex. [y1 y2 y3])for each flammable species in the mixture[.5 .5]input UFL in matrix form (ex. [UFL1 UFL2 UFL3])for each flammable species in the mixture[ ]UFLmix=https://www.osha.gov/dte/library/flammable_liquids/flammable_liquids.html
15Triangle DiagramsTriangle diagrams can be constructed using data provided for chemical species such the LFL, UFL, and LOC. The slope of the stoichiometric line can be calculated using the stoichiometry of the combustion reaction and the equation,The flammability zone can be approximated by using intersections of the limiting oxygen concentration, upper, and lower flammability limits. Triangle diagrams of various species can be constructed using the proper data.Crowl D A. Minimize the risks of flammable materials. Chemical engineering progress 2012;108(4):28-33.
16The triangle diagrams for propane and ethylene are shown.
17Limiting Oxygen Concentration This is the concentration of O2, in which below it, no combustion will occur even though there sufficient amount of fuelThe LOC has units of volume % of OxygenIt is determined by the same method of determining the LFL and UFL; the closed vessel apparatus.
18LOC and Oxygen mol Ratio Relationship From the stoichiometric combustion reactions, the mole ratio of oxygen to the combusting species can be obtained. A plot of the mol ratio and LOC suggests a logarithmic relationship between the two variables.
19LOC and Oxygen mol Ratio Relationship A correlation coefficient of suggests that there is somewhat of a relationship between the two variables.
20Plot of LOC vs O2 mol Ratio (no log) This graph depicts a linear relationship between the LOC and the oxygen mole ratio, and according to the previous matlab code, the correlation coefficient is , which is slightly less accurate than the Log-log relationship.
21LOC and Oxygen mol Ratio Relationship Plotting the logarithm of the LOC concentration versus the logarithm of the oxygen mol ratio of the reaction, the relationship can be observed.The equation for the line of best fit was calculated to beln(y) = ln(x) ,where y is the limiting oxygen concentration and x is the mole ratio.
22Flash PointThe flashpoint is the lowest temperature in which a vapor a vapor will form a mixture in the air that can ignite.At this point, the vapor will burn briefly, but it can lead to the fire point, where it will burn continuously.The flash point has to do with the vapor pressure of the substance, the measure of the concentration of vapor in equilibrium with the liquid.The higher the temperature, the higher the vapor pressure
23The Cleveland Open-Cup Tester to Determine Flash Point The way that the “Cleveland Open- Cup tester” works is first, the test cup of the apparatus (which is usually brass) is filled to a certain level with a portion of the product.Then, the temperature of this chemical is increased rapidly and then at a slow, constant rate as it approaches the theoretical flash point.The increase in temperature will cause the chemical to begin to produce flammable vapor in increasing quantities and density.The lowest temperature at which a small test flame passing over the surface of the liquid causes the vapor to ignite is considered the chemical's flash point.This apparatus may also be used to determine the chemical's fire point which is considered to have been reached when the application of the test flame produces at least five continuous seconds of ignition.Crowl D A. Minimize the risks of flammable materials. Chemical engineering progress 2012;108(4):28-33.
24Flashpoint Diagram and Significance The flashpoint occurs at a temperature at which the lowest concentration of vapor in a mixture with air can cause combustion. UFL and the flashpoint differ in temperature because the LFL is typically measured at room temperature, as indicated by the ambient temperature line. The UFL is the vapor concentration in combustion is not possible above. The Autoignition Zone is the point at which spontaneous combustion occurs without an outside source of energy.Crowl D A. Minimize the risks of flammable materials. Chemical engineering progress 2012;108(4):28-33.
25FlashpointThe boiling point of a hydrocarbon has a significant effect on the flashpoint of the species. A relationship between the flashpoint and boiling point is shown below.
26FlashpointVarious hydrocarbons boiling point and flashpoints were plotted along with the equation for estimating the flashpoint. The plot reveals a strong linear relationship between boiling point and flashpoint with a coefficient of correlation of approximately
27LFL and FlashpointA correlation coefficient of suggests a weak relationship exists between the two variables, LFL and Flashpoint.
28LFL and FlashpointA line of best fit for the logarithmic data is calculated to bey = x
29Minimum Ignition Energy This is the minimum amount of energy to ignite the fuel vapor.Typically a very small amount of energy is needed to ignite a vapor (0.025 mJ), and sparks that are detectable to the touch usually contain mJ of energy.These numbers indicate that the elimination of ignition sources is not a major way to prevent fire and explosion hazards
30Auto Ignition Temperature (AIT) This is the temperature where enough energy is available in the environment to provide an ignition source without an external source.To measure this, the flammable liquid is inserted into a preheated flask with a set temperature. It is observed for a set amount of time until, combustion behavior is observed.If nothing happens the temperature of the flask is raised until combustion behavior is observed.In this picture, the flammable chemical is injected inside the container to the right, and the temperature is adjusted accordingly to determine the autoignition temperature.
31AIT and the Shell Oil Refinery Explosion in Norco, Louisiana In 1988, a shell oil refinery in Norco,LA exploded due to a corrosion in one of the pipes in the Catalytic cracker unit.
32AIT and the Shell Oil Refinery Explosion in Norco, Louisiana (cont’d) A Catalytic Cracker Unit (CCU), is one of the most important units of an oil refinery. It is the unit that converts the high-boiling, and high molecular weight hydrocarbon fractions of petroleum crude oil into gasoline and other fuel products.
33AIT and the Shell Oil Refinery Explosion in Norco, Louisiana (cont’d) The feed containing long chain hydrocarbons and recycle slurry oil from the bottoms product of the distillation column enters the catalyst riser in the CCU. The catalyst riser contains hot powdered catalyst that mixes with the feed and breaks it into smaller molecules of vapor. After a few other processes, the product is extracted and the used catalyst enters the regenerator to be reactivated.
34AIT and the Shell Oil Refinery Explosion in Norco, Louisiana (cont’d) General process flow diagram of a CCU
35AIT and the Shell Oil Refinery Explosion in Norco, Louisiana (cont’d) High temperature fluids and high amounts of energy is handled when operating a CCU. In 1988 Norco,LA , corrosion tests were not implemented when a new elbow fitting was placed in the unit.Because of this, the fluid corroded the pipe and created an 8 inch hole in it. because of the high temperature, the vapor cloud ignited and caused an explosion that killed 7 people.The CCU diagram of Shell Oil at Norco indicating the failed elbowSource: Dick Hawrelak, The Shell Oil Norco VCE
36Prevent Fires From Flammable Materials Some fires and or explosions due to flammable materials can not be prevented totally, but can be reduced by:Storing them properlyInforming employees of high risk materialsPosting information about the possible dangerous materialLimit the amount of flammable materials on site.
37Storing Flammable Materials Safely Keep the flammable materials away from ignition sources, which include but are not limited to:Sparks from electrical equipment, or metals being cutTobacco smokeHot surfacesFire (open flame)
38What is an ideal storage area? Well ventilated, to avoid vapor concentrationFree of ignition sourcesCool temperature and dryEasily accessible by firefightersLabeled with warning signsAway from building exitsOn the ground floor, to make it easily accessible
39Limit The Amount of Flammable Materials on hand Keep only what you NEED on sitePurchase the flammable materials in the smallest volume necessaryDo not let the hazardous waste accumulateOnly keep the materials that are needed presently for the tasks being worked on.An example of a chemical storage that is not too big, and contains just what is needed for the task at hand.An example of a storage with too many flammable materials on hand.
40Increase Awareness Post warning signs Keep an active log of all flammable materials on handKeep MSDS sheets on hand for the flammable materialsInform people using the materials about flammability properties, such as:Upper Flammability Limit (UFL)Lower Flammability Limit (LFL)Minimum Ignition Energy (MIE)Limiting Oxygen Concentration (LOC)FlashpointIgnition Sources
41Proper Warning signsAppropriate safety signs should be put in instruction manuals and containers that contain flammable or explosive material.Flammable MaterialExplosive MaterialOxidizing Material
42Conclusion“Flammable materials can cause fires and explosions if they are not handled properly. Understanding these materials and risks they pose is the first step to mitigating fire hazards.”Out of the 100 chemical plant accidents, almost all of them were due to flammable materials.Understanding the flammability properties can help reduce the the hazards.Storing the flammable materials properly helps reduce the risk.Preventing fires/explosions caused by flammable materials is possible by understanding the properties of the materialsHundreds of lives can be saved.
43Future ImprovementsTo avoid fires and explosions, industries that handle flammable chemicals should hire third party inspectors to asses whether they are compliant to the government’s regulations (OSHA)More relationships between the properties of flammable materials should be studied and researched to see if there is a higher correlation with each other, to improve knowledge about flammable material to increase safety measures.Dr. Sam Mannan’s research includes flammability
44Referencescontent/uploads/2012/10/TheRelationshipbetweenFlashPointandLFLwithapplicatio ntoHybridMixturesLPS2007.pdfHristova, M., Tchaoushev, S. Journal of the University of Chemical Technology and Metallurgy. Calculation of Flash Points and Flammability Limits of Substances and Mixtures Journal.Crowl D A. Minimize the risks of flammable materials. Chemical engineering progress 2012;108(4):28-33.Dick Hawrelak, The Shell Oil Norco VCE, presented 1999https://fisher.osu.edu/blogs/macc-admissions/2010/11/02/whats-a-good-reference-for-your-application/