Noncondensible vapor

Process Description. Reactors used in the vapor-phase synthesis of thiophene and aLkylthiophenes are all multitubular, fixed-bed catalytic reactors operating at atmospheric pressure, or up to 10 kPa and with hot-air circulation on the shell, or salt bath heating, maintaining reaction temperatures in the range of 400—500°C. The feedstocks, in the appropriate molar ratio, are vaporized and passed through the catalyst bed. Condensation gives the cmde product mixture noncondensable vapors are vented to the incinerator. 

Shutting off steam at the completion of steam purging without admitting a noncondensible vapor (e.g., air at shutdown, fuel gas at startup). 

The toxicity and volume of some deoiled and dewatered sludge can be reduced further through thermal treatment. Thermal sludge treatment units use heat to vaporize the water and volatile components in the feed and leave behind a dry solid residne. The vapors are condensed for separation into hydrocarbon and water components. Noncondensable vapors are either flared or sent to the refinery amine nnit for treatment and nse as refinery fnel gas. 

Vapor binding, or air lock, is another common cause of household radiator malfunction. Often, the vapor accumulating in the radiator is CO,2, rather than air. The C02 originates from the thermal decomposition of carbonates in the boiler. Regardless, air and C02 form a noncondensable vapor in the radiator. These noncondensables mix with the steam in the radiator. The noncondensables then reduce the concentration of the steam, by dilution. The diluted steam has a lower partial pressure than pure steam. The lower the partial pressure of the steam, the more difficult it is to condense. As the rate of condensation of the steam drops, so does the heat radiated by the radiator. 

Provide a place from which noncondensable vapors may be vented Partial condensation... 

If we normally have a situation in which noncondensable vapors appear in the reflux drum, then there is only one pressure-control option available. This is to place the tower pressure-control valve on the vapor off-gas as shown in Fig. 13.9. If we normally have noncondensable vapors in the condenser effluent, then the following problems we have been discussing do not exist ... 

Sometimes we see tower pressure control based on feeding a small amount of inert or natural gas into the reflux drum. This is bad. The natural gas dissolves in the overhead liquid product and typically flashes out of the product storage tanks. The correct way to control tower pressure in the absence of noncondensable vapors is to employ flooded condenser pressure control. If, for some external reason, a variable level in the reflux drum is required, then the correct design for tower pressure control is a hot-vapor bypass. 

The second problem was air leaks. Air drawn into the system, would build up in the condenser. This noncondensable vapor was drawn off by using a steam jet. 

For a surface condenser to work properly, noncondensable vapors must be sucked out of llie shell side. This is done with a two-stage jet system, as shown in Fig. 18.3. When I was first commissioned the jets, they were unable to pull a good vacuum. Moreover, water periodically blew out of the atmospheric vent. I found, after considerable investigation, that the condensate drain line from the final condenser was plugged. 

The pressure in condenser A is greater than that in the surface condenser, and less than that in the final condenser (condenser B). This means that condenser A is operating at vacuum conditions. This prevents the condensed steam formed in condenser A from draining out to atmospheric pressure, unless the condenser is elevated by 10 to 15 ft. To avoid this problem, the condensate is drained back to the lower-pressure surface condenser. To prevent blowing the noncondensable vapors back to the surface condenser as well, a loop seal is required. The height of this loop seal must be greater than the difference in pressure (expressed in ft of water) between the surface condenser and the primary jet discharge condenser (condenser A). 

With the loop seal gone, the noncondensable vapors simply circulate around and around, through the primary jet, but no substantial vacuum in the surface condenser can be developed. 

The gas that accumulates inside the surface condenser is called the noncondensable load to the steam jets. Some of the noncondensable load consists of C02 accidentally produced when the boiler feedwater is vaporized into steam. Air leaks through piping flanges and valves are other sources of noncondensable vapors. But the largest source of noncondensable vapors is often air drawn into the turbine case, through the shaft s mechanical seals. To minimize this source of leaks, 2 or 3 psig of steam pressure is ordinarily maintained around the seals. However, as the turbine s shaft seals deteriorate, air in-leakage problems can overwhelm the jet capacity. This will cause a loss of vacuum in the surface condenser. 

These designs have provisions for the removal of noncondensable vapors and air, for the prevention of freezing during cold weather. Excessive buildup of noncondensable vapors in the main condenser would prevent effective condensation. Protection against ice formation is usually accomplished by warm air recirculation and/or fan control. Condensed steam from cooling coils flows by gravity to condensate receivers and is pumped back to the feedwater circuit by a condensate pump. 

FIGURE 11.19 Changes near liquid film when a noncondensible vapor is present in vapor. 

Shutting off purge steam without pressuring with noncondensable vapors... 

Gas the noncondensed vapors formed during the heating of the shale. 

The water and solvent vapors from the oil stripper and mineral oil stripper are typically condensed in a high vacuum condenser. The high vacuum condenser is a shell and tube vessel with the vapors typically on the shell side and the cooling water on the tube side. The noncondensable vapors are removed from the condenser by a steam ejector to maintain the 150-300-mm Hg absolute pressure on the shell side and are typically discharged into the first-stage evaporator for heat recovery. 

Ground corncobs. (2) Sulfuric acid. (3) Reactor. (4) Steam. (5) Residue. (6) Azeotropic distillation column. (7) Reboiler. (8) Heat exchangers. (9) Cooler. (10) Flash tank. (11) Noncondensible vapors. (12) Solids. 

A combination of characterization techniques for the pore structure of mesoporous membranes is presented. Equilibrium and dynamic methods have been performed for the characterisation of model membranes with well-defined structure while three-dimensional network models, combined with aspects from percolation theory can be employed to obtain structural information on the porous network topology as well as on the pore shape. Furthermore, the application of ceramic membranes in separations of condensable from noncondensable vapors is explored both theoretically and experimentally. 

The preflash column is used when the crude oil reaches a temperature of about 400—450 °F. At this point, some of the crude is above its boiling point, and vaporization occurs. The lightest portion of the crude is flashed (vaporized and separated from the bulk liquid) in the preflash column. The overhead is condensed and added into the atmospheric tower as a reflux, and the noncondensible vapors are added to the atmospheric tower overhead vapors. This step serves to conserve energy and unit investment for preheating the bulk of the crude. 

Particle formation can occur when two volatile and noncondensable vapor species react to form a product with an exceptionally low vapor pressure. Notable examples of atmospheric importance are the reactions of NH3 and HCl to produce NH4CI. The rate of nucleation of the product, say, NH4CI, depends on the concentrations of the reactants. To develop the nucleation theory in this case let us consider the NH3-HCI system. The NH3-HCI system can be represented as an equilibrium as... 

The seeond effect of drying on the environment arises from waste streams other than the products of combustion and heat, that is, dust and noncondensable vapors. 

Partial ixindenser Sometimes an overhead condenser is operated such that all of the vapor stream leaving the top plate in the colunm is not condensed, and the noncondensed vapor is withdrawn as the product instead of the condensed liquid as the product. Figure 8.1.24(a) illustrates this mode of operation. The overall and more volatile species molar balance equations for this condition over the dashed envelope crossing the column between the rath and (ra + l)th plate are ... 

Lean oil from the still is pumped through a heat exchanger and cooler and back to the absorber. Vapors from the still are cooled with partial condensation by indirect heat exchange with the rich oil. The condensate is passed to a separator, which removes water, and the liquid hydrocarbons are returned to the still as reflux. The partially cooled vapors are then passed to the benzol condenser where relatively complete condensation is obtained by the use of cooling water. In this particular plant, the condensate and noncondensed vapors are then passed through a vacuum pump to a separator. From this, noncondensed gases are returned to the fuel gas main, water condensate is removed for disposal, and the hydrocarbon layer is transferred to the crude-benzol storage tanks. 

Only noncondensable vapors should be discharged to atmosphere. 

Only noncondensable vapors should be discharged. (Pressure relief valves capable of venting liquids should discharge through a separator or flare drum so that the liquids are recovered, and also to prevent the liquids falling to the ground.)... 

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