Non-condensible gas

Still overhead—light naphthas. Steam and non-condensable gas 60-70... 

Figure 11. Vertical tube evaporator (A) Tube sheets (B) Downtake (C) Condensate outlet (D) Non-condensed gas outlet (E) Liquor inlet (F) Thick liquor outlet.

Figure 13. Steam outside tube evaporator (A) Shell (B) Tube sheets (C CJ Distributing plates (D) Vapor head (E) Baffles (F) Steam inlet (G) Condensate outlet (H) Non-condensed gas vent (J) Thick liquor outlet (K) Vapor outlet (L) Liquor feed box.

To prevent/reduce the undesirable condensation in the pump, a small hole is drilled in the pump head to admit air or other process non-condensable gas (gas ballast) into the latter portion of the compression stroke. This occurs while the vapor being compressed is sealed off from the intake port by the piston. By reducing the partial pressure of the vapor s condensables, the condensation is avoided. Obviously, this can reduce the capacity of the pump, as the leakage past the seals allows the gas ballast to dilute the intake volume of ba,se suction gas. For most process applications, the effect of this leakage is negligible, unless the vacuum system suction is below 1 torr [22]. 

Liquid height, ft = Non-condensable load factor = Latent heat of vaporization of steam, BTU/lb = Average mol weight of system vapors = Molecular weight of non-condensable gas = Molecular weight of condensable vapor = Total absolute pressure, Ibs/sq in. absolute (or other consistent units), or system operating pressure, torr... 

Partial pressure of air in mixture, Ibs/sq in. abs = Absolute intake pressure of pump = Piston displacement, cu ft/min = Partial pressure of non-condensable gas pounds per square inch absolute (or other absolute units)... 

Dmytryszyn, M., Condensation of a Condensable Vapor in the Presence of a Non-Condensable Gas, a thesis, Washington University, Sever Inst, of Technoloary, St. Louis, MO... 

The presence of non-condensable gases in steam systems (e.g. air and CO2) will reduce the partial pressure of the steam, and hence its temperature, thus affecting the output of the appliance. A further adverse effect is the presence of a non-condensable gas at the inside surface of a heat emitter. These impede condensation and, hence, heat output. It is therefore imperative that suitable means are provided to prevent formation of CO2 and to evacuate all gases from the system. 

Condenser fan stopped Non-condensible gas in system Pump strainer dirty (condenser water)... 

Wn = Weight of non-condensable gas, lbs/hr W, = Total pounds of mixture handled per hour Ws = Total steam consumption, ibs/hr W, = Weight of condensable vapor, lbs/hr Wt = Total weight of gas, lbs WTa = Total calculated air inleakage, lbs/hr or, WT = Total calculated air inleakage, lbs/hr... 

In considering the heat that is transferred, the method first put forward by NussELT(%i and later modified by subsequent workers is followed. If the vapour condenses on a vertical surface, the condensate film flows downwards under the influence of gravity, although it is retarded by the viscosity of the liquid. The flow will normally be streamline and the heal flows through the film by conduction. In Nusselt s work it is assumed that the temperature of the film at the cool surface is equal to that of the surface, and at the other side was at the temperature of the vapour. In practice, there must be some small difference in temperature between the vapour and the film, although this may generally be neglected except where non-condensable gas is present in the vapour. 

In the previous discussion it has been assumed that the vapour is a pure material, such as steam or organic vapour. If it contains a proportion of non-condensable gas and is cooled below its dew point, a layer of condensate is formed on the surface with a mixture of non-condensable gas and vapour above it. The heat flow from the vapour to the surface then takes place in two ways. Firstly, sensible heat is passed to the surface because of the temperature difference. Secondly, since the concentration of vapour in the main stream is greater than that in the gas film at the condensate surface, vapour molecules diffuse to the surface and condense there, giving up their latent heat. The actual rate of condensation is then determined by the combination of these two effects, and its calculation requires a knowledge of mass transfer by diffusion, as discussed in Chapter 10. 

For the condensation of a vapour in the presence of a non-condensable gas, the following example is considered which is based on an the work of Kern(28). 

The literature is replete with references to various foaming agents which are employed to lower permeability in steam swept zones. The vast majority of the foaming agents require the injection of a non-condensable gas to generate the foam in conjunction with the injection of steam and the foaming agent [1372]. 

Condensation from a non-condensable gas, where the gas is not soluble to any extent in the liquid condensed. These exchangers are often called cooler-condensers. 

Partial condensation. The methods developed for partial condensation and condensation from a non-condensable gas can be divided into two classes ... 

An assessment of the methods available for the design of condensers where the condensation is from a non-condensable gas is given by McNaught (1983). 

Fog formation. In the condensation of a vapour from a non-condensable gas, if the bulk temperature of the gas falls below the dew point of the vapour, liquid can condense out directly as a mist or fog. This condition is undesirable, as liquid droplets may be carried out of the condenser. Fog formation in cooler-condensers is discussed by Colburn and Edison (1941) and Lo Pinto (1982). Steinmeyer (1972) gives criteria for the prediction of fog formation. Demisting pads can be used to separate entrained liquid droplets. 

A radiochemical method for the determination of Rn-220 in fumarolic gas is studied. Both condensed water and non-condensing gas are collected together and Pb-212 is precipitated as PbS. After dissolving the precipitate in conc.HCI, it is mixed with an emulsion scintillator solution for activity measurements. As Pb-214 is simultaneously measured, the observed ratio of Pb-212 /Pb-214 gives Rn-220/Rn-222. This method is superior to the method of directly measuring Rn-220 for the samples in which Rn-220/Rn-222 ratios are less than unity. This method and the previously proposed direct method were applied in the field, and new data obtained. An attempt was also made to understand the formation and transport of radon underground. 

Formation and transport of radon ) In the present work, lead isotopes were chemically separated from the sample gas as lead sulfide since the formation of lead sulfide was inevitable under the presence of H2S in the fumarolic gas. The lead sulfide was then dissolved in a small amount of concentrated HCI and mixed with the Insta Gel(emulsion scintillator solution, Insta Gel, Packard Inc.) for the liquid scintillation counting. The chemical yield and the volume of the collected non-condensing gas were obtained from the measurement of the activities of Pb-214 and its progeny which were in radioequilibrium with their precursor Rn-222 whose concentration was determined separately by the direct method. 

Non-Condensable Gas Accumulation If noncondensible gases are not removed, overpressure can result when a heat exchanger surface becomes blanketed or pressure drop through the condensers is increased by the presence of the non-condensable gas. 

Gasification is the conversion by partial oxidation at elevated temperature of a carbonaceous feedstock into a gaseous energy carrier consisting of permanent, noncondensable gases. Ideally, the process produces only a non-condensable gas and an ash residue. However, since gasification processes are carried out far from equilibrium, tars (condensable organic material) are produced and the ash resi-... 

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