Wet gases

Calculating the hydrate formation temperature is essential when one needs to guard against equipment and line plugging that can result when wet gas is cooled, intentionally or not, below 30°C. 

The four vertical lines on the diagram show the isothermal depletion loci for the main types of hydrocarbon gas (incorporating dry gas and wet gas), gas condensate, volatile oil and black oil. The starting point, or initial conditions of temperature and pressure, relative to the two-phase envelope are different for each fluid type. 

Gas is produced to surface separators which are used to extract the heavier ends of the mixture (typically the components). The dry gas is then compressed and reinjected into the reservoir to maintain the pressure above the dew point. As the recycling progresses the reservoir composition becomes leaner (less heavy components), until eventually it is not economic to separate and compress the dry gas, at which point the reservoir pressure is blown down as for a wet gas reservoir. The sales profile for a recycling scheme consists of early sales of condensate liquids and delayed sale of gas. An alternative method of keeping the reservoir above the dew point but avoiding the deferred gas sales is by water injection. 

Wet gas unprocessed or partially processed natural gas produced from strata containing condensible hydrocarbons. 

It is generally unacceptable to emit sulfur dioxide, thus the scmbber effluent must be treated for sulfur dioxide removal. If the plant aheady possesses faciUties for the production of sulfuric acid, this rather concentrated sulfur dioxide stream can be easily fed into the wet gas cleaning circuit and disposed of in the sulfuric acid plant. The quantity is so small that it does not put any additional burden on the sulfuric acid plant. Because no tellurium is carried over with the selenium dioxide during roasting, it is possible to produce a selenium product which can be purified to commercial grade (99.5-99.7%). 

In general, plants using SO2 gas derived from metallic sulfides, spent acids, or gypsum anhydrite purify the gas stream before drying it by cold, ie, wet, gas purification. Various equipment combinations including humidification towers, reverse jet scmbbers, packed gas cooling towers, impingement tray columns and electrostatic precipitators are used to clean the gas. 

Wet gas scmbbing, which is highly effective for SO removal, is much less effective for NO removal. Because NO in the flue gas is 90—95% NO and because NO has a relatively low solubiUty in absorbing solutions, Htfle NO is removed (47). 

A wet gas meter such as No. S-39465, E. H. Sargent and Company, is satisfactory. This meter need not be a permanent part of the apparatus. It is used only to calibrate the flowmeter. 

Three types of anodic protection can be distinguished (1) impressed current, (2) formation of local cathodes on the material surface and (3) application of passivating inhibitors. For impressed current methods, the protection potential ranges must be determined by experiment (see information in Section 2.3). Anodic protection with impressed current has many applications. It fails if there is restricted current access (e.g., in wet gas spaces) with a lack of electrolyte and/or in the... 

Basically, a gas absorption tower is a unit in which the desirable light ends components are recovered from the gas feed by dissolving them in a liquid passing through the tower countercurrently to the gas. The liquid absorbent is called lean, oil, and it usually consists of a hydrocarbon fraction in the gasoline boiling range. After the absorption step, the liquid which now contains the desired constituents in solution is referred to as fat oil. A similarly descriptive nomenclature is applied to the gas, which is referred to as wet gas when it enters the tower and as dry gas when it leaves the absorber. 

Figure 8-4 shows a typical trayed contactor in which the gas and liquid are in counter-current flow. The wet gas enters the bottom of the contactor and contacts the "richest glycol (glycol containing water in solution)... 

The lean glycol concentration leaving the reboiler can be lowered by contacting the glycol with stripping gas. Often, wet gas that is saturated with water vapor at ambient temperature and 25 to 100 psig is used. Al 25 psig and 100°F this gas is saturated with 1,500 Ib/MMscf of water vapor. At atmospheric pressure and the temperatures in the reboiler the gas can absorb over 100,000 Ib/MMscf. 

In the adsorption cycle, the wet inlet gas flows downward through the tower. The adsorbable components are adsorbed at rates dependent on their chemical nature, the size of their molecules, and the size of the pores. The water molecules are adsorbed first in the top layers of the desiccant bed. Dry hydrocarbon gases are adsorbed throughout the bed, As the upper layers of desiccant become saturated with water, the water in the wet gas stream begins displacing the previously adsorbed hydrocarbons in the lower desiccant layers. Liquid hydrocarbons will also be absorbed and will fill pore spaces that would otherwise be available for water molecules. 

Once the bed has been dried in this manner, it is necessary to flow c(X)l gas through the tower to return it to normal operating temperatures (about 100°F to 120°F) before placing it back in service to dehydrate gas. The cooling gas could either be wet gas or gas that has already been dehydrated. If wet gas is used, it must be dehydrated after being used as cooling gas. A hot tower will not sufficiently dehydrate the gas. 

The temperature of the regeneration gas that commingles with the incoming wet gas ahead of the dehydrators is also important. If the tem perature of these two gas streams differs more than 15°F to 20°F, liquid water and hydrocarbons will condense as the hotter gas stream cools. I hc condensed liquids can shorten the solid desiccant life. 

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