Erosive Effect of Gas Flow

Burning, Erosive(in Propellants)(Erosive Effect of Gas Flow or Erosion of Propellants). Mansell (Ref 1) was one of the first to observe that the rate of burning inside tubular proplnts was faster than that on the outside. A similar phenomenon was observed later by Muraour(Ref 2). No importance was attached to this phenomenon until it was observed also(but on a larger scale) in rocket motors during and after WWII(Ref 11)... 

Several theories have been proposed for explanation of the erosive effect of gas flow in proplnts(See Refs 4,5,7 13)... 

The expander turbine is designed to minimize the erosive effect of the catalyst particles stiU remaining in the flue gas. The design ensures a uniform distribution of the catalyst particles around the 360° aimulus of the flow path, optimizes the gas flow through both the stationary and rotary blades, and uses modem plasma and flame-spray coatings of the rotor and starter blades for further erosion protection (67). 

Particle-laden multiphase flows, usually turbulent, cover a wide range of applications, such as pollution control, sediment transport, combustion processes, erosion effects in gas turbines, and so on. One of the most important aspects of particle-laden turbulent flows is the mutual interactions between particles and turbulence. PIV techniques, as a powerful tool other than numerical simulation method and theoretical analysis, have been applied to this research field of particle-laden multiphase flows. Note that, dispersed-phase particles in particle-laden... 

Erosion is the deterioration of a surface by the abrasive action of solid particles in a liquid or gas, gas bubbles in a liquid, liquid droplets in a gas or due to (local) high-flow velocities. This type of attack is often accompanied by corrosion (erosion-corrosion). The most significant effect of a joint action of erosion and corrosion is the constant removal of protective films from a metal s surface. This can also be caused by liquid movement at high velocities, and will be particularly prone to occur if the solution contains solid particles that have an abrasive action. 

VFO works well in gas turbines. In a nine-month test program, the combustion properties of VFO were studied in a combustion test module. A gas turbine was also operated on VFO. The tests were conducted to study the combustion characteristics of VFO, the erosive and corrosive effects of VFO, and the operation of a gas turbine on VFO. The combustion tests were conducted on a combustion test module built from a GE Frame 5 combustion can and liner. The gas turbine tests were conducted on a Ford model 707 industrial gas turbine. Both the combustion module and gas turbine were used in the erosion and corrosion evaluation. The combustion tests showed the VFO to match natural gas in flame patterns, temperature profile, and flame color. The operation of the gas turbine revealed that the gas turbine not only operated well on VFO, but its performance was improved. The turbine inlet temperature was lower at a given output with VFO than with either natural gas or diesel fuel. This phenomenon is due to the increase in exhaust mass flow provided by the addition of steam in the diesel for the vaporization process. Following the tests, a thorough inspection was made of materials in the combustion module and on the gas turbine, which came into contact with the vaporized fuel or with the combustion gas. The inspection revealed no harmful effects on any of the components due to the use of VFO. 

The lift pipe design was tapered to a larger diameter at the top. This minimized the effects of erosion and catalyst attrition, and also prevented the instantaneous total collapse of circulations when the saltation concentration, or velocity, of solids is experienced (i.e. the slump veloeity-that velocity helow which particles drop out of the flowing gas stream). In a typical operation, 2 % to 4 % eoke can he deposited on the catalyst in the reactor and burned in the regenerator. Catalyst circulation is generally not sufficient to remove all the heat of eombustion. This facilitated the need for steam or pressurized water coils to be located in the regeneration zone to remove exeess heat. 

The simultaneous action of erosive wear and corrosion is called erosion corrosion. Erosion corrosion is often encountered in pumps and pipes exposed to turbulent flow in the presence of suspended particles. It also occurs in other situations, for example in incinerators due to ash particles that are entrained by the exhaust gas. The damage caused by the combined effect of the impingement of a liquid and of corrosion is sometimes referred to as impingement corrosion or impingement attack. 

Direct exhaust-gas impingement (erosion corrosion) can occur due to the high-velocity exhaust gas stream on the internal surfaces of the exhaust system. This effect is important at sharp bends and surfaces normal to the gas flow. The combination of particulate matter with hot corrosive gas produces this type of attack. 

Conveying of solids over long distances up to a few thousand feet encoimters different phenomena owing to the gas expansion of that distance. The gas expansion caused the gas and solid velocities to increase and thus affect the attrition of the particles and the erosion of the pipeline, both of which increase to the nth power with velocity, where n ranges from 2.5 to 5.0. To slow the particles down, one can step the pipeline to larger diameters to decrease the velocities. Another technique developed in our laboratories is to use a flow economizer, which effectively takes gas from the system in a prescribed fashion to reduce the gas velocity. Figure 4 shows a schematic of the flow economizer tested in our laboratory. This unit withdraws a prescribed amount of air at critical points in the transport line. 

Erosion of the outer surface of the gas outlet tube or vortex finder can occur from several possible causes and we will briefly discuss each of these below. Perhaps the most obvious cause is direct impaction, which can occur if any part of the vortex finder lies in the projected path of the particles entering the cyclone. See Fig. 12.1.3a. As shown in Fig. 12.1.3b, the incoming gas can be expected to constrict, either due to the geometry or due to the effect of the gas already rotating in the cyclone and flow around the gas outlet tube. But this is not always the case for the solids. 

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