Vapor containment loss

Under certain conditions, such as hyperbaria,airway heat losses can account for a considerable percentage of total body heat production (in some cases > 100%). Normally these threats are ameliorated by rapid moderation of inspired air temperature and humidity by exchanging heat and water vapor between the mucus and airstream in the upper airway. Recovering much of the heat and water vapor contained in expired air minimizes heat and water losses to the ambient environment and aids in whole-body thermoregulation. 

Tight Container A tight container protects the contents from contamination of extraneous liquids, solids, or vapors from loss of the chemical and from efflorescence, deliquescence, or evaporation under the ordinary or customary conditions of handling, shipment, storage, and sale, and is capable of tight reclosure. 

In the development of a new process, it will be necessary to fractionate 910 kg/h of an ethanol-water solution containing 0.3 mole fraction ethanol. It is desired to produce a distillate containing 0.80 mole fraction ethanol, with negligible loss of ethanol in the residue, using a sieve-tray distillation column at atmospheric pressure. Preliminary calculations show that the maximum vapor-volumetric flow rate occurs at a point in the column just above the feed tray, where the liquid and the vapor contain 0.5 and 0.58 mole fraction of ethanol, respectively. The temperature at that point in the column is about 353 K the local slope of the equilibrium curve is m = 0.42. The liquid and vapor molar flow rates are 39 and 52 kmol/h, respectively. 

The vapor contains components that can condense out and are undesirable in the liquid in excessive quantities vaporized liquid losses in the gas are of little economic consequence This case is identical to case 2 above, except that the condensation is not maximized but is set (usually manually) at a rate that will ensure that the undesirable components remain in the vapor. This case occurs when the product value of the gas is much the same as the liquid, or if the vaporized liquid is recovered from the gas in a downstream facility. As in case 2, the control systems in Figs. 17.4a- and 17.7c are suitable. 

The vapor contains components that can condense out and are undesirable in the liquid in excessive quantities vaporized liquid losses in the gas incur a significant economic penalty Here excessive condensation will render the liquid product off-spec on lights insufficient condensation will cause too much liquid product to escape in the vapor stream, incurring an economic penalty. In this case, in addition to column pressure control, the rate of condensation must be controlled to obtain the desired vapor-liquid split. This case is perhaps the most common in the chemicals industry and is discussed in detail below. 

The wide use of liquid oxygen as an oxidant in rocket engines has resulted in an increased interest in low-temperature heat transfer. Storage tanks for this type of application, being uninsulated, contain a boiling-liquid low-temperature sink, which is susceptible to environmental heat inputs and subsequent liquid loss by vaporization. Such losses are difficult to predict due to the complex combination of ambient conditions which exist and the lack of knowledge concerning their combined effects. 

Loss of Vapor Containment in Large Vapor Degreasers... 

LOSS OF VAPOR CONTAINMENT IN LARGE VAPOR DEGREASERS... 

Mobil s High Temperature Isomerization (MHTI) process, which was introduced in 1981, uses Pt on an acidic ZSM-5 zeoHte catalyst to isomerize the xylenes and hydrodealkylate EB to benzene and ethane (126). This process is particularly suited for unextracted feeds containing Cg aHphatics, because this catalyst is capable of cracking them to light paraffins. Reaction occurs in the vapor phase to produce a PX concentration slightly higher than equiHbrium, ie, 102—104% of equiHbrium. EB conversion is about 40—65%, with xylene losses of about 2%. Reaction conditions ate temperature of 427—460°C, pressure of 1480—1825 kPa, WHSV of 10—12, and a H2/hydtocatbon molar ratio of 1.5—2 1. Compared to the MVPI process, the MHTI process has lower xylene losses and lower formation of heavy aromatics. 

A typical m el ter iastalled in a medium sized brass foundry contains 4500 kg of brass and its inductor is rated 500 kilowatts. Brass is an alloy containing copper and zinc. Zinc vaporizes at temperatures weU below the melting temperature of the alloy. The channel iaductor furnace s low bath temperature and relatively cool melt surface result in low metal loss and reduced environmental concerns. Large dmm furnaces have found use in brass and copper continuous casting installations. 

Most small Hquid helium containers are unpressurized heat leak slowly bods away the Hquid, and the vapor is vented to the atmosphere. To prevent plugging of the vent lines with solidified air, check valves of some sort are included in the vent system. Containers used for air transportation are equipped with automatic venting valves that maintain a constant absolute pressure with the helium container in order to prevent Hquid flash losses at the lower pressures of flight altitudes and to prevent the inhalation of air as the pressure increases during the aircraft s descent. Improved super insulation has removed the need for Hquid nitrogen shielding from almost all small containers. 

Ferritic stainless steels depend on chromium for high temperature corrosion resistance. A Cr202 scale may form on an alloy above 600°C when the chromium content is ca 13 wt % (36,37). This scale has excellent protective properties and occurs iu the form of a very thin layer containing up to 2 wt % iron. At chromium contents above 19 wt % the metal loss owiag to oxidation at 950°C is quite small. Such alloys also are quite resistant to attack by water vapor at 600°C (38). Isothermal oxidation resistance for some ferritic stainless steels has been reported after 10,000 h at 815°C (39). Grades 410 and 430, with 11.5—13.5 wt % Cr and 14—18 wt % Cr, respectively, behaved significandy better than type 409 which has a chromium content of 11 wt %. 

Because of the relative instabiUty of FeO, the reduction to metallic Fe occurs at a much lower temperature and appreciable CO2 is present in the product gas. The high temperature required for the reaction of MnO and C results in the formation of essentially pure CO the partial pressures of CO2 and Mn are <0.1 kPa (1 X 10 atm). The product of this reaction is manganese carbide (7 3) [12076-37-8J, Mn C, containing 8.56% carbon. Assuming immiscibility of the metal and carbide, Mn should be obtainable by the reaction of MnO and Mn C at 1607°C. However, at this temperature and activity of Mn, the partial pressure of Mn vapor is approximately 10 kPa (0.1 atm) which would lead to large manganese losses. 

The dichlorobenzene isomers have very similar vapor pressures making separation by distillation difficult. Crystallization is generally used in combination with distillation to obtain the pure 1,2 and 1,4-dichlorobenzene isomers. The small quantity of 1,3-dichlorobenzene isomer produced is not generally isolated as a pure product. Environmental concerns have led to the use of improved crystalliza tion systems that contain the products with minimal losses to the environment. 

Most storage containers for ciyogens are designed for a 10 percent ullage volume. The latter permits reasonable vaporization of the contents due to heat leak without incurring too rapid a buildup of the pressure in the container. This, in turn, permits closure of the container for short periods of time to either avoid partial loss of the contents or to transport flammable or hazardous ciyogens safely from one location to another. 

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