Topping turbines

P. Todtenhaupt [547] investigated the homogenization characteristic of a stirred column with 5 stirrers on the same shaft and flow from bottom to the top. Turbine, cross-beam, MIG and propeller stirrers were used. The stirred column was provided with round baffles, but did not possess partition trays between the individual stirred sections. Turbine stirrers performed the best and propeller stirrers conveying downwards the worst. For these two stirrer types the following process relationships apply ... 

TOPPING TURBINE - Have been used when old boilers are replaced with new high pressure boilers. The turbine is a backpressure turbine exhausting to the old boiler header still supplying steam to the old lower pressure turbines. 

Five principal drivers are used for multistage centrifugal compressors. These include condensing turbines, topping turbines, electric motors, gas turbines, and steam turbines. Electric motor drives generally are used in regions where cheap power is available. Steam turbines are usually inexpensive to operate and can provide up to 18,000 rpm. Condensation turbines usually run at lower speeds of between 10,000 to 14,000 rpm, while gas turbines tend to be the most expensive to operate and usually run in the range of 5,000-6,000 rpm. 

The approximate size of the unit may be arrived at by the quality-factor method referred to in Fig. T-72. By applying an appropriate-size factor, the topping turbine may in this case be designed for an efficiency of, say, 67 percent, corresponding to a quality factor of about 4500. With an available enthalpy drop of 147 Btu the sum of the velocity squares is 660,000. Because of the comparatively small volume flow and the high density of the steam, small wheel diameters are used thus the bucket speed is rather low. If we assume, for instance, 350 ft/s, corresponding to about... 

In this accident, the steam was isolated from the reactor containing the unfinished batch and the agitator was switched ofiF. The steam used to heat the reactor was the exhaust from a steam turbine at 190 C but which rose to about 300°C when the plant was shutdown. The reactor walls below the liquid level fell to the same temperature as the liquid, around 160°C. The reactor walls above the liquid level remained hotter because of the high-temperature steam at shutdown (but now isolated). Heat then passed by conduction and radiation from the walls to the top layer of the stagnant liquid, which became hot enough for a runaway reaction to start (see Fig. 9.3). Once started in the upper layer, the reaction then propagated throughout the reactor. If the steam had been cooler, say, 180 C, the runaway could not have occurred. ... 

The General Mills mixer—settler (117), shown in Figure 13b, is a pump—mix unit designed for hydrometaHurgical extraction. It has a baffled cylindrical mixer fitted in the base and a turbine that mixes and pumps the incoming Hquids. The dispersion leaves from the top of the mixer and flows into a shallow rectangular settler designed for minimum holdup. 

In apphcation to electric utihty power generation, MHD is combined with steam (qv) power generation, as shown in Figure 2. The MHD generator is used as a topping unit to the steam bottoming plant. From a thermodynamic point of view, the system is a combined cycle. The MHD generator operates in a Brayton cycle, similar to a gas turbine the steam plant operates in a conventional Rankine cycle (11). 

Eig. 8. Cost of electricity (COE) comparison where represents capital charges, Hoperation and maintenance charges, and D fuel charges for the reference cycles. A, steam, light water reactor (LWR), uranium B, steam, conventional furnace, scmbber coal C, gas turbine combined cycle, semiclean hquid D, gas turbine, semiclean Hquid, and advanced cycles E, steam atmospheric fluidized bed, coal E, gas turbine (water-cooled) combined low heating value (LHV) gas G, open cycle MHD coal H, steam, pressurized fluidized bed, coal I, closed cycle helium gas turbine, atmospheric fluidized bed (AEB), coal J, metal vapor topping cycle, pressurized fluidized bed (PEB), coal K, gas turbine (water-cooled) combined, semiclean Hquid L, gas turbine... 

Another example of a topping cycle cogeneration system is one based on recovering the thermal energy exhausting from a gas turbine/generator. 

Pitched-blade turbines (Fig, 18-3) are used on top-entering agitator shafts instead of propellers when a high axial circulation rate is desired and the power consumption is more than 2,2 kW (3 hp), A pitched-blade turbine near the upper surface of liquid in a essel is effecth e for rapid submergence of floating particulate solids,... 

For Reynolds numbers greater than 2000 baffles are commonly used with turbine impelTers and with on-centerhne axial-flow impellers. The flow patterns illustrated in Figs. 18-15 and 18-16 are quite different, but in both cases the use of Baffles results in a large top-to-bottom circulation without vortexing or severely unbalanced fluid forces on the impeller shaft. 

Coal is fed as a paste containing 25 wt % water, and sorbent is fed diy by a lock-hopper system with pneumatic conveying. The top size of each feedstock is 3 mm in). The latent heat lost evaporating the water fed with the paste is compensated by increased gas turbine power output resulting from the increased flue-gas mass flow rate. For the 80-MWe unit, there are six coal feed points (one per 4.5 m" [48 ft"]) and four sorbent feed points (one per 6.7 m" [72 ft"]), all entering beneath the tube bank along one wall. The bed depth is... 

Figure 4-29. 360-t/d packaged unit—top foundation plate 13 m long, 3.6 m wide, 0.93 m high. The oil system is situated at the front end, followed by the steam turbine, compressor, and expander. The oil coolers are located separately. 

External Combustor (experimental). The heat exehanger used for an external-combustion gas turbine is a direct-fired air heater. The air heater s goal is to achieve high temperatures with a minimum pressure decrease. It consists of a rectangular box with a narrow convection section at the top. The outer casings of the heater consist of carbon steel lined with lightweight blanket material for insulation and heat re-radiation. 

Both top and bottom halves of the journal bearings should be inspected for misalignment wear as well as excessive in-line wear, which can occur in turbines with frequent starts. An indication of the condition of the thrust-bearings can be made by removing a small section of the turbine shaft, usually on the governor end, and axially moving or bumping the shaft. The amount of axial shaft movement will indicate the thrust clearance and, if it is found to be 0.012-0.015 inches, it can be considered normal. 

In the ease where the turbine and supports have a minimal eross seetion, then the ability to inerease the stiffness of these pedestals is minimized. Consequently, the objeetive is to eoneentrate on inereasing the mass of the pedestals. This inerease is aeeomplished by filling the eavities with a speeial mortar prepared with epoxy and steel shot. The density of this speeial mortar ean be in exeess of 300 pounds per eubie foot. To injeet this speeial mortar, a pipe has been installed in the aeeess hole that was drilled in the side of the pedestal near the top. These same teehniques ean be employed to stabilize the foundations under mueh smaller equipment. 

Top entering mixers are heavy duty equipment. They are usually fixed to a rigid structure or tank mounting. Either radial flow or axial flow turbines may be used. Speeds vary from 50 to 100 rpm and usually require a double set of helical gearing or a single set of worm gears to achieve these low speeds. Therefore, they are more expensive than single reduction mixers. 

On top of this alloy development, turbine blades for the past two decades have been routinely made from single crystals of predetermined orientation the absence of grain boundaries greatly enhances creep resistance. Metallic monocrystals have come a long way since the early research-centred uses described in Section 4.2.1. 

A top entering pitched blade turbine having w/D = 1/8 is appropriate for this blending service. 

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