| 6-1. | Estimate the flash point of a solution of 50 mol % water and 50 mol % methanol. |
| 6-2. | Estimate the flash point of a solution of 50 mol % water and 50 mol % ethanol. |
| 6-3. | Estimate the LFL and the UFL of the following mixtures:
| | All in volume % |
|---|
| | a | b | c | d |
|---|
| Hexane | 0.5 | 0.0 | 1.0 | 0.0 | | Methane | 1.0 | 0.0 | 1.0 | 0.0 | | Ethylene | 0.5 | 0.5 | 1.0 | 1.0 | | Acetone | 0.0 | 1.0 | 0.0 | 1.0 | | Ethyl ether | 0.0 | 0.5 | 0.0 | 1.0 | | Total combustibles | 2.0 | 2.0 | 3.0 | 3.0 | | Air | 98.0 | 98.0 | 97.0 | 97.0 |
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| 6-4. | Estimate the LFL and the UFL of Problem 6-3a at 50°C, 75°C, and 100°C. |
| 6-5. | Estimate the UFL of Problem 6-3a at 1 atm, 5 atm, 10 atm, and 20 atm of pressure. |
| 6-6. | Estimate the LFL and the UFL using the stoichiometric concentrations for methane, propylene, ethyl ether, and acetone. Compare these estimates to actual values. |
| 6-7. | Estimate the LOC of propane, hydrogen, and methane. |
| 6-8. | Determine the LOC of a mixture of 2% hexane, 3% propane, and 2% methane by volume. |
| 6-9. | Determine the minimum compression ratio required to raise the temperature of air over hexane to its AIT. Assume an initial temperature of 100°C. |
| 6-10. | What will be the LFL of hexane in the presence of hexane mists with drops larger than 0.01 mm? |
| 6-11. | Why do staged hydrogen compressors need interstage coolers? |
| 6-12. | Why do hot engines sometimes continue to run after the ignition is turned off? |
| 6-13. | A set of experiments is run on a flammable gas in a spherical vessel. The following data are obtained for two different vessel volumes. Estimate the value of KG for this combustible gas:
| V = 1 m3 | V = 20 m3 |
|---|
| Time (s) | P (bar) | Time (s) | P (bar) |
|---|
| 0.0 | 0.0 | 0.0 | 0.0 | | 0.1 | 0.2 | 0.2 | 0.15 | | 0.2 | 0.5 | 0.3 | 0.35 | | 0.3 | 1.2 | 0.4 | 0.6 | | 0.35 | 1.6 | 0.5 | 0.9 | | 0.40 | 3.2 | 0.6 | 1.4 | | 0.425 | 4.7 | 0.7 | 2.2 | | 0.450 | 6.5 | 0.8 | 4.1 | | 0.475 | 6.9 | 0.85 | 5.0 | | 0.500 | 7.1 | 0.90 | 6.2 | | 0.550 | 7.4 | 0.95 | 7.1 | | 0.600 | 7.3 | 1.00 | 7.0 | | 0.650 | 7.0 | 1.05 | 7.2 | | 0.700 | 6.4 | 1.10 | 6.7 | | 0.750 | 6.1 | 1.15 | 6.25 | | 0.800 | 5.7 | 1.20 | 5.90 | | 0.900 | 5.1 | 1.30 | 5.40 | | 1.000 | 4.7 | 1.40 | 5.00 | | | | 1.50 | 5.60 |
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| 6-14. | Determine the energy of explosion for 1 lb of gaseous n-butane. What is the TNT equivalent? |
| 6-15. | A gas cylinder contains 50 lb of propane. The cylinder accidentally falls over and ruptures, vaporizing the entire contents of the cylinder. The cloud is ignited and an explosion occurs. Determine the overpressure from this explosion 100 ft away. What type of damage is expected? |
| 6-16. | A VCE with methane destroyed a house structure 100 ft away from the ignition source. Estimate the amount of methane released. |
| 6-17. | A large cloud of propane is released and eventually ignited, producing a VCE. Estimate the quantity of propane released if the blast shattered windows 3 mi from the source of the ignition. |
| 6-18. | At 77°F gasoline has a vapor pressure of 4.6 psia. Why can gasoline be stored in vented storage vessels without the presence of flammable vapors above the liquid in the vessel? Comment on the EPA’s effort to reduce gasoline volatility in order to reduce fugitive emissions. What will happen as the volatility is reduced? |
| 6-19. | An automobile assembly line includes an operation that involves filling the gas tanks with gasoline. Estimate the ventilation rate required to reduce the vapors from this operation to below the LFL for gasoline. Assume that each tank has a volume of 14 gal and that a tank can be filled in 3 min. Assume splash filling and that only one tank is filled at a time. The molecular weight of gasoline is about 94, and its vapor pressure at 77°F is 4.6 psia. Also, calculate the ventilation air required to reduce the concentration of the gasoline vapors to below the TLV-TWA. Which problem is more difficult? |
| 6-20. | A butane tank is located 500 ft from a residential area. Estimate the minimum instantaneous release of butane required to produce a vapor concentration in the residential area equal to the LFL for butane. What continuous release rate is required? Assume that the release occurs at ground level. Will the minimum amount increase, decrease, or stay the same if the release occurs above ground level? |
| 6-21. | Benzene is stored in an inside storage area, 15 ft long and 15 ft wide with an 8-ft ceiling. This storage area has a ventilation system that changes the air in the room completely six times per hour. The storage area is also equipped with a flammable vapor detector that sounds an alarm when the flammable vapor concentration reaches 25% of the LFL for benzene. What is the minimum benzene spill rate, in lb/hr, that will set off the flammable vapor alarm in the room? Assume a pressure of 1 atm and a temperature of 80°F. Also assume average ventilation conditions. |
| 6-22. | A standard laboratory cylinder is about 5 ft high with an internal vessel diameter of about 6 in. Determine the total energy of explosion for this cylinder if it contains nitrogen compressed to 2500 psig. Assume initial and ambient conditions of 298 K and 1 atm. |
| 6-23. | Many chemical operators believe that the inerted vapors above a flammable liquid are not flammable when they mix with air. This is frequently not the case: If the inerted vapors escape from the vessel and mix with air or if the vessel is purged with air after emptying, the resulting mixture might be flammable.
A storage vessel contains liquid benzene at 100°F. The vessel vapor space is inerted with pure nitrogen to a total pressure of 1/2-in of water gauge. Assume that the vapor space is saturated with benzene vapor.
Determine the volume percent concentration of benzene in the vapor. Use a flammability diagram to show whether this mixture will become flammable or not when mixed with air. (Hint: 1 atm = 34.4 ft of water.)
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| 6-24. | An informal industry rule is to design occupied control rooms to withstand a 1- ton blast of TNT at 100 ft.
What overpressure does this correspond to? What quantity (in pounds) of propane (C3H8) does this correspond to, based on an equivalent amount of energy? How far away (in ft) from this 1- ton blast must a residential home be in order to receive no more than minor damage to house structures?
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| 6-25. | According to fire code, propane storage tanks cannot be closer than 10 ft from a house. This requirement is designed to prevent flammable vapors from entering the house, not to protect the house from a potential explosion.
What quantity of propane (in lbm) can be stored under these conditions that will cause no more than minor damage to a house in the event of an explosion? Be sure to list any assumptions. |
| 6-26. | Fires and explosions are substantial hazards in many chemical plants.
Describe with examples the three ingredients of any fire. Create a checklist with at least six items to identify fire hazards in any workplace. List six common fire prevention/protection features for chemical plants, and describe when they would be appropriate.
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| 6-27. | The following liquids are stored in a storage vessel at 1 atm and 25°C. The vessels are vented with air. Determine whether the equilibrium vapor above the liquid will be flammable. The liquids are:
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| 6-28. | A natural gas wellhead is located 400 m from an instrument control room. The control room is a potential ignition hazard in the event of a leak of natural gas (essentially pure methane). Studies have shown that a suitable safety margin is imposed if the downwind gas concentration is determined using one-half the LFL. For methane this represents a concentration of 2.5 vol. %.
What is the minimum release rate of methane (in kg/s) that will result in a concentration at the control room equal to half the LFL? Be sure to state your assumptions clearly. Assume a temperature of 298 K and an ambient pressure of 1 atm. If the methane pressure in the wellhead is at 10 atm pressure, what hole size (in cm) will produce the release rate of part a? If the largest pipe size in the wellhead is 4 cm (internal diameter), comment on the likelihood of an ignition hazard from the control room.
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| 6-29. | In the TWA Flight 800 tragedy the accident is blamed on explosion of fuel vapors in the central fuel tank. The volume of the central fuel tank is 18,000 gal.
If, at the time of the explosion, the fuel concentration in the tank is 1% by volume and the pressure inside the tank is 12.9 psia, determine the equivalent energy of explosion for the vapor (in pounds of TNT). Assume a temperature of 80°F. Be sure to state carefully any assumptions. Estimate the overpressure at a distance of 50 ft from the fuel tank explosion from the explosion of the vapors in part a. Estimate the limiting oxygen concentration (LOC) for the jet fuel, given that the LFL is 0.6% by volume and the stoichiometric coefficient for oxygen in the combustion equation is 18.9.
For jet fuel the energy of explosion is 18,590 Btu/lb and the molecular weight is 160. |
| 6-30. | You have decided to purchase a 500-gal tank of liquid propane (C3H8) to heat your house during the winter. You are concerned about tank rupture and the possibility of a vapor cloud explosion of all the propane. How far away (in ft) must the tank be from the house to ensure that your house will receive only minor damage from an explosion? The specific gravity of liquid propane is 0.500, and the energy of explosion for propane is 503.9 kcal/g-mol. |
| 6-31. | A liquid mixture containing 0.50 mole fraction benzene-toluene is contained in a storage vessel at 25°C and 1 atm. The vessel is vented to the atmosphere.
Is the vapor in the vessel flammable? What are your resulting concerns about fire and explosion hazards with this storage vessel?
Hint: Benzene-toluene can be assumed to be an ideal liquid-vapor system. |
| 6-32. | A tank containing liquid butane (C4H10) is located 500 ft from an electrical substation. One of the scenarios we are considering is the breaking of a 1-in schedule 40 pipe (internal diameter = 1.049 in) with discharge of the liquid butane. We are concerned that this leak will cause flammable vapor concentrations at the substation. Assume that all the liquid flashes to vapor.
Estimate the discharge rate (in lbm/s) of butane from the 1-in broken pipe. Estimate the butane vapor concentrations at the substation. Is this likely to be a flammable hazard?
The temperature is 80°F and the ambient pressure is 1 atm. Make sure you clearly state any assumptions. The vapor pressure of liquid butane at 80°F is 40 psia, and the specific gravity of liquid butane at 80°F is 0.571. |
| 6-33 | Acetone is used as a solvent in a laboratory. There is some concern about the fire hazards associated with the acetone. One solution is to dilute the pure acetone with water, thus providing an increased flash point. What mole fraction of water in a water-acetone mixture is required to increase the flash point of the mixture to 100°F? Acetone is completely soluble in water. |
| 6-34 | You have been assigned the task of assisting in relocating the new control room for your process. The new control room will be designed to withstand an explosive overpressure of 2 psig. Your attention is focused on a propane storage tank located 100 m from the proposed site for the new control room. What is the maximum quantity of propane (in kg) that can be stored in this tank without exceeding the overpressure rating of the control room? Make sure you state any assumptions used in your calculation. |
| 6-35. | Methyl alcohol liquid is stored in a vessel. Its vapor is inerted with nitrogen to a total pressure of 2 in of water gauge. Will the inerted vapor be flammable if it escapes the vessel? Assume a temperature of 25°C. |
| 6-36. | Draw a flammability diagram for n-butane. The experimentally reported LOC for n-butane is 12%. What must the oxygen concentration be reduced to before pumping in butane? What butane concentration must the vapor be reduced to before pumping air into the vessel before taking it out of service? |
| 6-37. | For flammable gases the minimum ignition energy is typically 0.1 mJ. The mass of a penny is typically 2.6 g. How far must this penny be dropped to contain the kinetic energy equal to 0.1 mJ? |
| 6-38. | During a particular accident, an estimated 39,000 kg of flammable material was released and ignited, resulting in an explosion and fireball and the subsequent fatalities and equipment damage. The publication Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and BLEVES (New York: American Institute of Chemical Engineers, 1994) provides a number of equations useful for estimating the effects of such an explosion.
The heat radiation intensity (in kW/m2) from a ball of burning vapor is given by the empirical equation
The effective time duration (in seconds) of the burn is given by
The height of the center of the fireball (in meters) is assumed to be constant during the burn and is given by
Finally, the maximum diameter of the fireball (in meters) is given by
For these equations Ie is the effective radiation intensity (kW/m2), mf is the mass of fuel (kg), L is the distance from the center of the fireball to the receptor (m), and te is the effective time duration of the burn (s).
Use a spreadsheet program (such as Quattro Pro or Excel) to estimate the total number of fatalities resulting from the burning fireball. Use the probit equations provided in the text. Assume that 400 people are distributed evenly at a distance of 75 m to 1000 m from the fireball center. Divide the distance interval into a number of small increments. Use a small enough distance increment so that the results are essentially independent of the increment size.
Your spreadsheet output should have designated columns for the distance from the fireball center, radiation intensity, probit values, and percentage and number of fatalities. You should also have a single designated spreadsheet cell providing the total number of fatalities.
One way to simplify the procedure is to specify a threshold radiative flux. It is assumed that 100% fatalities will occur to anyone exposed to anything above this value. Anyone exposed to a lesser value will be unharmed. Estimate an approximate threshold radiative flux value that will result in the same number of fatalities as the detailed probit calculation. |
| 6-39. | The air in a 55-gal drum must be flushed and inerted with nitrogen before the drum is filled with a flammable liquid. This is accomplished by placing a nitrogen lance through the hole of the drum reaching to the bottom. A constant flow rate of nitrogen is used to achieve the inerting.
Show that the concentration of oxygen in the drum is represented by
where C is the concentration of oxygen in the drum (mass/volume), k is the nonideal mixing factor (0.1 < k < 1), and Qv is the volumetric flow of nitrogen (volume/time). Show that the time required to reach a target concentration Cf from an initial concentration Co is given by
Estimate the time it will take to inert a drum to 1% oxygen using 75 L/min of nitrogen. Use k as a parameter.
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| 6-40. | A container in a process using a flammable vapor has dimensions of 100 m by 100 m by 10 m high. Use the TNO multi-energy model to estimate the overpressure 100 m from the process resulting from the release and ignition of the flammable vapor. Assume that 20% of the process volume is moderately congested and that the remaining 80% is lightly congested. Be sure to state any additional assumptions. |
