Explosive Range

The removal of volatile organic compounds (VOC) from air is most often accompHshed by TSA. Air streams needing treatment can be found in most chemical and manufacturing plants, especially those using solvents. At concentrations from 500 to 15,000 ppm, recovery of the VOC from steam used to regenerate activated carbon adsorbent thermally is economically justified. Concentrations above 15,000 ppm ate typically in the explosive range and... 

A central location where instmment leads are short is preferred. In modem faciHties with distributed control systems, all units are controUed from a central control room with few operators. Only a few roving operators are available to spot trouble. It is desirable to deep process equipment a minimum of 8 m away from the control room. Any equipment and hydrocarbon-containing equipment should be separated by at least 15 m if possible. Most control rooms are designed with blastproof constmction and have emergency backup power and air conditioning. The room is pressuri2ed to prevent infusion of outside air that may have hydrocarbon content in the explosive range. 

The catalyst temperature is about 1100°C. Precious metal catalysts (90% Pt/10% Rh in gauze form) are normally used in the commercial processes. The converters are similar to the ammonia oxidation converters used in the production of nitric acid (qv) although the latter operate at somewhat lower temperatures. The feed gases to the converter are thoroughly premixed. The optimum operating mixture of feed gas is above the upper flammabiUty limit and caution must be exercised to keep the mixture from entering the explosive range. 

Testing conditions are not as constrained as for catalysts in an existing production unit, but other conditions may set some limits, like explosive range, start of a homogeneous reaction, corrosion, polymerization, etc. Literature should be searched for this limitation, in addition to other information on the main reaction. Literature gives much more information if interest is not limited to the main reaction but is extended to analogous processes as well. 

The atmosphere in gasoline tanks is too rich in hydrocarbons, and in kerosene tanks is too lean in hydrocarbons, so that theoretically, both mixtures of air and vapor are outside the explosivity range. 

The volatile solvents recoverable by the activated carbon system or any other system are nearly all organic, and many of them form flammable or explosive mixtures with air. Such mixtures may lie between upper and lower explosive limits. The activated carbon system can avoid the explosive range by staying well below the lowest percentage of vapor which is still explosive it functions well at very low concentrations. The system also recovers solvents efficiently even in the presence of water the recovery efficiency is high (98 percent and 99 percent are not unusual) it may be fully automatic. The annual maintenance charge rarely exceeds 5 percent of the cost of equipment. The recovery expense may be as low as 0.2 cent per pound in some installations it rarely exceeds 1 cent per pound. 

Figure 5-12. An attempt to avoid explosions by passing quickly through the explosive range was not successful.

Flammable Limits The minimum and maximum concentration of fuel vapor or gas in a fuel vapor or gas/gaseous oxidant mixture (usually expressed in percent hy volume) defining the concentration range (flammable or explosive range) over which propagation of flame will occur on contact with an ignition source. See also Lower Flammable Limit and Upper Flammable Limit. 

Rapid release of energy dirough die ignition of atmospheric mixtures of flanuiiable gases, vapors or combustible dusts widiiii the explosive range... 

C. Operation in or near flammable range covers for the possibility of air mixing with material in equipment or storage tanks, under conditions where the mixture will be within the explosive range. 

The most significant hazard of this process is the probability of an explosion if the concentration of ammonia in the reactor is inadvertently allowed to reach the explosive range, > 14 per cent. 

The extreme hazards involved in handling this highly reactive material are stressed. Freshly distilled material rapidly polymerises at ambient temperature to produce a gel and then a hard resin. These products can neither be distilled nor manipulated without explosions ranging from rapid decomposition to violent detonation. The hydrocarbon should be stored in the mixture with catalyst used to prepare it, and distilled out as required [1], The dangerously explosive gel is a peroxidic species not formed in absence of air, when some l,2-di(3-buten-l-ynyl)cyclobutane is produced by polymerisation [2], The dienyne reacts readily with atmospheric oxygen, forming an explosively unstable polymeric peroxide. Equipment used with it should be rinsed with a dilute solution of a polymerisation inhibitor to prevent formation of unstable residual films. Adequate shielding of operations is essential [3],... 

A detonation wave is a very rapid wave of chemical reaction which, once it is initiated, travels at a stable supersonic speed, called the detonation velocity, in a high explosive. Typically, detonation velocities for pressed or cast high explosives range from... 

The ideal solution is to perform a risk analysis for each item in a facility to determine the probable maximum fire and explosive range the location may produce. The calculations and expense to accomplish such a task today does not appear to justify a unilateral application to every piece of equipment at a facility. Consequentially the use of a spacing table for a facility design provides for an economical and expedient solution. This is especially important when several options on the layout of the facility are available. However in some instances the use of risk analysis may demonstrate less spacing is necessary that what a spacing chart requires. 

Flammable (explosive) Range The range of gas or vapor concentration (percentage by volume in air) that will burn or explode if an ignition source is present. Limiting concentrations are commonly called the lower explosive limit and the upper explosive limit. Below the lower explosive limit, the mixture is too lean to burn above the upper explosive limit, the mixture is to rich to burn. 

Upper Explosive Limit Also known as Upper Flammable Limit. Is the highest concentration (expressed in percent of vapor or gas in the air by volume) of a substance that will burn or explode when an ignition source is present. Theoretically above this limit the mixture is said to be too rich to support combustion. The difference between the LEL and the UEL constitutes the flammable range or explosive range of a substance. That is, if the LEL is one ppm and the UEL is five ppm, then the explosive range of the chemical is one ppm to Five ppm. (See also LEL)... 

Hydrazine vapor, explosive range of, 73 587 Hydrazine-water azeotrope, breaking, 73 579... 

Table IV presents a summary of the explosive range for the experiments reported by Porteous and Reid. Although there is a spread of Tn/T i somewhat beyond the 1.00-1.10 range noted above, in most cases there is excellent agreement.

Fixed bed plants. In this type of plant, the process flow for all three feeds looks like the plant in Figure 20—3. The feed and compressed air are mixed, vaporized in a heater, and then charged to the fixed-bed reactor, a bundle of rubes packed with the catalyst. The ratio of air to hydrocarbon is generally about 75 1 to keep the mixture outside the explosive range, always a good idea. The feed temperature is 800-900°F, depending on the feed. The reaction time is extremely quick, so the feed is in contact with the catalyst for only 0.1 to 1.0 second. 

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