Steam velocity

The metal loss and resulting split were caused by erosion from impingement of high-velocity steam in which droplets of water were entrained. The conical pinnacles in the affected region are typical of deterioration by this mechanism. 

Close examination of each circular spot revealed a small forest of erosion cones (Fig. 11.35). Erosion was caused by the impingement of high-velocity steam probably mixed with droplets of condensate. The circular, equally spaced erosion sites apparently reproduced corresponding, equally spaced circular openings in the exhaust inlet. Compare Case History 11.3. 

Condensers should be designed to provide a realistic amount of excess auxiliary exhaust steam with reasonable velocity steam inlets and exhausts. Also, steam baffles should be slanted away from condenser bracing and other critical areas. 

Turbine designers had been experimenting with machines in which the blades were driven by a high-velocity steam jet that expanded through them in a single stage. It had been shown that steam-jet velocities of the order of 1000 m/s were required. 

Impulse turbine design employs a stationary, circular diaphragm onto which a large number of fixed-position, tear-shaped nozzle blades (vanes) are mounted. High-velocity steam moves across the vanes and produces steam jets that are directed into waterwheel-type buckets, mounted onto discs around the turbine rotor. The pressure of the steam in the buckets forces the shaft to rotate. The kinetic energy of the jets is translated into mechanical work as the shaft turns. 

A type of metal wastage caused by the mechanical action abrasion of the metal surface by high velocity steam, air bubbles or solid particles. Often part of a larger erosion-corrosion process. 

High velocity steam or particles striking a metal surface and causing metal wastage by erosion. Also refers to unbumed fuel oil striking a surface and resulting in the formation of carbon deposits and smoke. 

For corrosion and safety reasons, the condensate recovered from these sources is best not returned to the deaerator for use as boiler feedwater. However, depending on the contaminant, the condensate may be reused for a number of services. Our favorite reuse of such contaminated condensate is as a replacement for velocity steam in the heater-tube passes of a fired furnace. 

Similarly, as the high-velocity steam enters the mixing chamber shown in Fig. 16.1, it produces an extremely low pressure. The gas flows from the jet suction nozzle and into the low-pressure mixing chamber. It is not correct to say that the gas is entrained by the steam. The gas just flows into the mixing chamber, because there is a very low pressure in the mixing chamber. 

The high-velocity steam strikes the buckets around the rim of the turbine wheel shown in Fig. 17.1. Actually, these so-called buckets resemble blades or vanes. I imagine the term bucket is a carryover from the days of the water wheel. The velocity of the steam is now transferred to the spinning turbine wheel. If the turbine is running below its set speed, the speed controller causes the governor speed-control valve to open. 

The partially dehydrated fryer then passes through a de-oiler, where some of the oil from the surface of the product is blown off by high-velocity steam, air, or nitrogen at high temperature. 

For lowest capital cost, the preheat furnace is usually a dry operation. Sometimes, however, two or three percent weight of superheated steam is added to the feed to give a higher internal velocity, thus reducing the rate of carbon laydown inside the tubes. This steam is termed velocity steam to differentiate... 

Usually, steam is added to the preheat system, either as velocity steam or after the preheater as dilution steam to get deeper volatilization. Each product is steam stripped as in crude oil distillation. In the case of naphthenic crude oils, the bottom product may be directed to asphalt specialties rather than being treated to make lubricating oil base stock. 

The 1-1/4-inch thermowell can, because of its large size thread, be provided with a thicker tapered-wall construction which starts at the bottom of the threads it is shown in Figure 7-88a. It is used for higher pressure, temperature and velocity steam services, because of its sturdy construction. 

Heating tube temperature Bed temperature Minimum fluidizing velocities Steam temperature Steam velocity Coal feed rate (wb)... 

Inadequate velocity steam. Steam is injected into the vacuum furnace coils to promote vaporization by reducing the hydrocarbon partial pressure. 

FIGURE 13-8 Velocity steam suppressess peak temperatures. 

It seems as if the vacuum-lower transfer line is a weak point in many crude units. It is possible, because of an incorrectly sized transfer line, to approach sonic velocity in these lines. Such superhigh velocities have led to rapid erosion and failure of the transfer line. If a unit s transfer line is experiencing an accelerated rate of failures, the operating engineer should consider several questions. Has the flash-zone pressure been substantially reduced Has the furnace charge rate (including velocity steam) been increased Is the vacuum-tower feed lighter than it used to be ... 

Colder cooling water lor ejector condensers Seal-weld HVGO and TOO drawoff trays Increase the number of bottom-stripping trays More superheat of exhaust stripping steam Add velocity steam... 

Coking cycles, 33-72 Coking heater, 73-80, 89 mass ve-locily/heat flux, 75 feed interruption, 75-77 velocity steam, 77 sodium, 77-78 light resid, 78 foamover, 78 parallel passes, 78 steam-air decoking, 78-79 online spalling, 79-80 run length, 89... 

Most coking heaters have several thousand pounds per hour of high-pressure steam injected into the heater tubes. The velocity steam should increase the linear velocity of resid in the lubes, shorten oil residence time, and hence reduce the thermal soaking time to which the resid is exposed. This ought to reduce the formation of coke in the heater tubes. In practice, there seems little correlation between the amount of velocity steam used and the rale at which coke builds up in the lubes. 

Apparently, the steam flows at a high velocity through the center of the tubes, while the liquid resid creeps relatively slowly along the tube walls. This is called annular flow. The principal benefit from velocity steam may be to help sweep resid out of the tubes during a feed interruption. At mass velocities greater than 400 Ib/ft /sec, most refiners do not use velocity steam. 

Low mass velocity Feed interruptions Stuttering resid flow Loss of velocity steam Sodium salts Light resid Foamovers... 

Reduced flash-zone pressure Lighter feed More velocity steam Increased charge rate Furnace tube peaking temperature... 

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