Gas pressure drops

To find the line size for the most economical pressure drop (gases only) ... 

Inlet pressure and pressure drop (gas-phase reactions)... 

TWO-PHASE FLOW PRESSURE DROP (GAS-LIQUID) ESTIMATION... 

Figure 11.10(b) can be modeled as a piston flow reactor with recycle. The fluid mechanics of spouting have been examined in detail so that model variables such as pressure drop, gas recycle rate, and solids circulation rate can be estimated. Spouted-bed reactors use relatively large particles. Particles of 1 mm (1000 pm) are typical, compared with 40-100 pm for most fluidizable catalysts. 

Counter-current gas/vapor-liquid film flows in SP above the load conditions are extremely complicated. For this reason, it appears improbable that the CFD-based virtual experiments replace real experiments entirely in the near future. However, even single-phase CFD simulations can improve predictivity of pressure drop models, since all correlations pressure drop - gas load used in practice contain some dry pressure drop correlation as a basic element. Replacing this correlation by the rigorous CFD analysis helps to avoid heuristic assumptions on possible correlation structure, which are inevitable both in conventional mechanistic models (Rocha et ah, 1993) and in more sophisticated considerations (Olujic, 1997). 

Figure 8. Typical pressure drop-gas rate curve obtained at steady state in bead pack tests.

Figure 3.36. Pressure drop-gas velocity relationship and characteristic of fluidised-bed reactors [63]...

The fluctuation in gas rate is also associated with fine flow induced by great change in PEL. Coal from this well presents in block, with some in powder (Fig. 2(b)), which is controlled by faults within the study area. The extreme change in PEL leads to quick pressure drop, gas desorption within reservoir near wellbore, and thus the high gas rate in a short time. However, quick and fluctuate drainage system can contribute to coal fine concentration increase in fluid, fine accumulation in pore and finally a dramatic gas rate decrease after present fine production, gas rate will increase in a short time as a result of the better permeability and conductivity. 

Gas-liquid For large liquid holdup, slow reactions that are kinetically controlled reactions that require long residence times and low viscosity liquids. Preferred if large gas volumes needed or if the liquid vol > 40 m OK for high pressure. Cocurrent surface area 50-400 m /m Downflow surface area 20-1000 m /m. Ha < < 0.3 and = 4000-10000. Can handle solids. Incurs a high pressure drop. Gas-liquid-catalytic solid Surface area 50-350 m /m. ... 

Hydrodynamics in gas-liquid systems have been studied extensively in the past due to their wide range of applications. Characteristics of interest include flow regimes, local pressure drop, gas residence time, axial diffusion coefficients, bubble size, bubble rise velocity, gas holdup, and power consumption. This section will summarize various experimental techniques to quantify some of these characteristics. 

Macrokinetic processes for trickle-bed reactors are summarized on Table 9. The main features are the hydrodynamics of fluid flows (flow regimes, pressure drops, gas-liquid-solid interfacial areas, radial distribution of fluids), the state of macromixing of fluids and the heat transfer between the reactor and the environment. All these processes may again be correlated versus the energy dissipated into the reactor, and their knowledge... 

In addition to the S/C (and O/C), other key parameters to be defined in the design and operation of an external reformer in the system include gas space velocity, pressure drop, gas inlet temperature, and gas exit temperature. 

Indeed, a major obstacle to the development of foam catalysts is the lack of reliable engineering correlations for the relevant morphological and transport properties, which also prevents a conclusive appraisal of their potential in comparison to other more or less conventional structures. Four interlinked areas are of interest in this respect, associated with the description of the foam geometry, as well as of pressure drop, gas/solid mass and heat transfer, and overall (axial and radial) heat transfer in foam catalytic structures, respectively. An exhaustive review of the technical literature on foam catalysts is beyond the scope of the present chapter, so only the most significant published contributions to these topics are summarized in the next paragraphs. 

This tendency for preferential gas flows (near the walls) could cause serious problems in systems where the reaction is either strongly exothermic or endothermic, because the uneven temperature distribution may aggravate these bypass phenomena [71,72]. On viewing moving-bed systems within the framework of a fixed coordinate system, it is readily apparent that the linear velocity of the solids is much smaller than that of the gas. It follows that in predicting pressure drop-gas flow relationships, heat and mass transfer coefficients, and the like, we may use the correlations that were previously given in Section 7.3 for fixed-bed systems. 

Once the bubble point is reached (at point B), the first bubble of ethane vapour is released. From point B to C liquid and gas co-exist in the cell, and the pressure is maintained constant as more of the liquid changes to the gaseous state. The system exhibits infinite compressibility until the last drop of liquid is left In the cell (point C), which is the dew point. Below the dew point pressure only gas remains in the cell, and as pressure is reduced below the dew point, the volume increase is determined by the compressibility of the gas. The gas compressibility is much greater than the liquid compressibility, and hence the change of volume for a given reduction in pressure (the... 

Using this mixture as an example, consider starting at pressure A and isothermally reducing the pressure to point D on the diagram. At point A the mixture exists entirely in the liquid phase. When the pressure drops to point B, the first bubble of gas is evolved, and this will be a bubble of the lighter component, ethane. As the pressure continues to drop, the gas phase will acquire more of the heavier component and hence the liquid volume decreases. At point C, the last drop of liquid remaining will be composed of the heavier component, which itself will vaporise as the dew point is crossed, so that below... 

The initial condition for the dry gas is outside the two-phase envelope, and is to the right of the critical point, confirming that the fluid initially exists as a single phase gas. As the reservoir is produced, the pressure drops under isothermal conditions, as indicated by the vertical line. Since the initial temperature is higher than the maximum temperature of the two-phase envelope (the cricondotherm - typically less than 0°C for a dry gas) the reservoir conditions of temperature and pressure never fall inside the two phase region, indicating that the composition and phase of the fluid in the reservoir remains constant. 

For both volatile oil and blaok oil the initial reservoir temperature is below the critical point, and the fluid is therefore a liquid in the reservoir. As the pressure drops the bubble point is eventually reached, and the first bubble of gas is released from the liquid. The composition of this gas will be made up of the more volatile components of the mixture. Both volatile oils and black oils will liberate gas in the separators, whose conditions of pressure and temperature are well inside the two-phase envelope. 

Black oils are a common category of reservoir fluids, and are similar to volatile oils in behaviour, except that they contain a lower fraction of volatile components and therefore require a much larger pressure drop below the bubble point before significant volumes of gas are released from solution. This is reflected by the position of the iso-vol lines in the phase diagram, where the lines of low liquid percentage are grouped around the dew point line. 

When fluid flow in the reservoir is considered, it is necessary to estimate the viscosity of the fluid, since viscosity represents an internal resistance force to flow given a pressure drop across the fluid. Unlike liquids, when the temperature and pressure of a gas is increased the viscosity increases as the molecules move closer together and collide more frequently. 

Viscosity is measured in poise. If a force of one dyne, acting on one cm, maintains a velocity of 1 cm/s over a distance of 1 cm, then the fluid viscosity is one poise. For practical purposes, the centipoise (cP) is commonly used. The typical range of gas viscosity in the reservoir is 0.01 - 0.05 cP. By comparison, a typical water viscosity is 0.5 -I.OcP. Lower viscosities imply higher velocity for a given pressure drop, meaning that gas in the reservoir moves fast relative to oils and water, and is said to have a high mobility. This is further discussed in Section 7. 

Reservoirs containing low compressibility oil, having small amounts of dissolved gas, will suffer from large pressure drops after only limited production. If the expansion of oil is the only method of supporting the reservoir pressure then abandonment conditions (when the reservoir pressure is no longer sufficient to produce economic quantities of oil to the surface) will be reached after production of probably less than 5% of the oil initially in place. Oil compressibility can be read from correlations. 

Oil viscosity is an important parameter required in predicting the fluid flow, both in the reservoir and in surface facilities, since the viscosity is a determinant of the velocity with which the fluid will flow under a given pressure drop. Oil viscosity is significantly greater than that of gas (typically 0.2 to 50 cP compared to 0.01 to 0.05 cP under reservoir conditions). 

As the reservoir pressure drops from the initial reservoir pressure towards the bubble point pressure (PJ, the oil expands slightly according to its compressibility. However, once the pressure of the oil drops below the bubble point, gas is liberated from the oil, and the remaining oil occupies a smaller volume. The gas dissolved in the oil is called the solution gas, and the ratio of the volume gas dissolved per volume of oil is called the solution gas oil ratio (Rg, measured in scf/stb of sm /stm ). Above the bubble point, Rg is constant and is known as the initial solution gas oil ratio (Rgj), but as the pressure falls below the bubble point and solution gas is liberated, Rg decreases. The volume of gas liberated is (Rg - Rg) scf/stb. 

If, however, the reservoir pressure drops below the bubble point, then gas will be liberated in the reservoir. This liberated gas may flow either towards the producing wells under the hydrodynamic force imposed by the lower pressure at the well, or it may migrate... 

For direct measurement from core samples, the samples are mounted in a holder and gas is flowed through the core. The pressure drop across the core and the flowrate are measured. Providing the gas viscosity (ji) and sample dimensions are known the permeability can be calculated using the Darcy equation shown below. 

Gas has a much higher compressibility than oil or water, and therefore expands by a relatively large amount for a given pressure drop. As underground fluids are withdrawn (i.e. production occurs), any free gas present expands readily to replace the voidage, with only a small drop in reservoir pressure. If only oil and water were present in the reservoir system, a much greater reduction in reservoir pressure would be experienced for the same amount of production. 

Solution gas drive occurs in a reservoir which contains no initial gas cap or underlying active aquifer to support the pressure and therefore oil is produced by the driving force due to the expansion of oil and connate water, plus any compaction drive.. The contribution to drive energy from compaction and connate water is small, so the oil compressibility initially dominates the drive energy. Because the oil compressibility itself is low, pressure drops rapidly as production takes place, until the pressure reaches the bubble point. 

In the solution gas drive case, once production starts the reservoir pressure drops very quickly, especially above the bubble point, since the compressibility of the system is low. Consequently, the producing wells rapidly lose the potential to flow to surface, and not only is the plateau period short, but the decline is rapid. 

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