Compressor diffuser

Water injection, or steam injection systems, are being used extensively to augment power. Corrosion problems in the compressor diffuser and combustor have not been found to be major problems. The increase in work and efficiency with a reduction in NO makes the process very attractive. Split-shaft cycles are attractive for use in variable-speed mechanical drives. The off-design characteristics of such an engine are high efficiency and high torque at low speeds. 

Deniz, S., Greitzer, E. and Cumpsty, N., 1998, Effects of Inlet Flow Field Conditions on the Performance of Centrifugal Compressor Diffusers Part 2 Straight-Channel Diffuser, ASME Paper No. 98-GT-474. 

Likewise, the cold legs connect the PCUs at the elevation of the compressor outlets. Flow is collected from the compressor diffuser, and approximately 90% of the flow at 140°C crosses in the cold leg and enters the top of an annular ring of coolers to flow downward, to be cooled, and then to go directly into the next compressor inlet. Approximately 10% of the cold flow is b3 assed upward to flow through an annulus around the hot-leg duct, so the hot-leg pressure boundary is maintained at the same temperature as the cold-leg boundary to minimize thermal stresses due to the PCU vessels being connected at two elevations by cross-over legs. The cold cross-over leg eliminates the vessel volume and pressure drop that... 

Compressor rotor assembly Stator blades, rotor blades Compressor case assembly Air inlet filter assembly Bearings and seals Compressor diffuser assembly... 

Successful operation of the gaseous diffusion process requires a special, fine-pored diffusion barrier, mechanically rehable and chemically resistant to corrosive attack by the process gas. For an effective separating barrier, the diameter of the pores must approach the range of the mean free path of the gas molecules, and in order to keep the total barrier area required as small as possible, the number of pores per unit area must be large. Seals are needed on the compressors to prevent both the escape of process gas and the inflow of harm fill impurities. Some of the problems of cascade operation are discussed in Reference 16. 

From equation 60 one can obtain a theoretical power requirement of about 900 kWh/SWU for uranium isotope separation assuming a reasonable operating temperature. A comparison of this number with the specific power requirements of the United States (2433 kWh/SWU) or Eurodif plants (2538 kWh/SWU) indicates that real gaseous diffusion plants have an efficiency of about 37%. This represents not only the barrier efficiency, the value of which has not been reported, but also electrical distribution losses, motor and compressor efficiencies, and frictional losses in the process gas flow. 

Fouling Industrial streams may contain condensable or reactive components which may coat, solvate, fill the free volume, or react with the membrane. Gases compressed by an oil-lubricated compressor may contain oil, or may be at the water dew point. Materials that will coat or harm the membrane must be removed before the gas is treated. Most membranes require removal of compressor oil. The extremely permeable poly(trimethylsilylpropyne) may not become a practical membrane because it loses its permeability rapidly. Part of the problem is pore collapse, but it seems extremely sensitive to contamination even by diffusion pump oil and gaskets [Robeson, op. cit., (1994)]. 

Combustors All gas turbine combustors perform the same function They increase the temperature of the high-pressure gas at constant pressure. The gas turbine combustor uses veiy little of its air (10 percent) in the combustion process. The rest of the air is used for cooling and mixing. The air from the compressor must be diffused before it enters the combustor. The velocity leaving the compressor is about 400-500 ft/sec (130-164 m/sec), and the velocity in the combustor must be maintained at about 10-30 ft/sec (3-10 iTi/sec). Even at these low velocities, care must be taken to avoid the flame to be carried downstream. To ensure this, a baffle creates an eddy region that stabi-hzes the flame and produces continuous ignition. The loss of pressure in a combustor is a major problem, since it affecls both the fuel consumption and power output. Total pressure loss is in the range of 2-8 percent this loss is the same as the decrease in compressor efficiency. 

Axial-Flow Compressors. An axial-flow eompressor eompresses its working fluid by first aeeelerating the fluid and then diffusing it to obtain a pressure inerease. The fluid is aeeelerated by a row of rotating airfoils or blades (the rotor) and diffused by a row of stationary blades (the stator). The... 

All gas turbine combustors perform the same function, they increase the temperature of the high-pressure gas. The gas turbine combustor uses very little of its air (10%) in the combustion process. The rest of the air is used for cooling and mixing. New combustors are also circulating steam for cooling purpose. The air from the compressor must be diffused before it enters the... 

Diffusion-blading loss. This loss develops because of negative velocity gradients in the boundary layer. Deceleration of the flow increases the boundary layer and gives rise to separation of the flow. The adverse pressure gradient that a compressor normally works against increases the chances of separation and causes significant loss. 

Recirculating loss. This loss occurs because of backflow into the impeller exit of a compressor and is a direct function of the air exit angle. As the flow through the compressor decreases, there is an increase in the absolute flow angle at the exit of the impeller as seen in Figure 6-34. Part of the fluid is recirculated from the diffuser to the impeller, and its energy is returned to the impeller. 

Most centrifugal compressors in service in petroleum or petrochemical processing plants use vane less diffusers. A vaneless diffuser is generally a simple flow channel with parallel walls and does not have any elements inside to guide the flow. 

Boyce, M.P., and Bale, Y.S., Diffusion Loss in a Mixed-Flow Compressor, Intersociety Energy conversion Engineering conference, San Diego, Paper No. 729061, September 1972. 

Johnston, R. and Dean, R., 1966, Losses in Vaneless Diffusers of Centrifugal Compressors and Pumps, ASME Journal of Basic Engineering, Vol. 88, pp. 49-60. 

Klassen, H.A., Effect of Inducer Inlet and Diffuser Throat Areas on Performance of a Low-Pressure Ratio Sweptback Centrifugal Compressor, NASA TM X-3148, Lewis Research Center, January 1975. 

Rodgers, C., Influence of Impeller and Diffuser Characteristic and Matching on Radial Compressor Performance, SAE Preprint 268B, January 1961. 

Rodgers, C., 1982, The Perfoimance of Centrifugal Compressor Channel Diffusers, ASME Paper No. 82-GT-lO. 

Lieblein, S., Schwenk, F.C., and Broderick, R.L., Diffusion Factor for Estimating Losses and Limiting Blade Loading in Axial-Flow Compressor Blade Elements, NACA RM 53001 (1953). 

---