Pipeline feeding devices

By the nature of the feeding mechanism, rotary valves are more suited to relatively nonabrasive materials. This is particularly the case where they are used to feed materials into positive pressure conveying systems. By virtue of the pressure difference across the valve, and the need to maintain a rotor tip clearance, air will leak across the valve. Wear, therefore, will not only occur by conventional abrasive mechanisms, but by erosive wear also. Air leakage through the blade tip clearances can generate high velocity flows, which will entrain fine particles, and the resulting erosive wear can be far more serious than the abrasive wear. Wear resistant materials can be used in the construction of rotary valves, and removable 

For positive pressure conveying systems it is usual to have a small opening in the side of the rotary valve so that the air leaking across the valve can be vented. The vented air is usually directed to the supply hopper above, where it can be filtered, for this air can carry fine material with it. To increase the pressure capability of rotary valves, end plates are usually fitted to the rotors and the radial surfaces are provided with seals in order to minimise the air leakage. 

This high pressure type of feeder, however, is only suitable for fine materials, such as cement and fine grades of fly ash, that are capable of being compressed to a higher bulk density in the reducing pitch section of the screw, since this is how the air seal is achieved. As a consequence of this the power required to drive the screw is quite high. 

A consequence of the reduction in flow area is an increase in air velocity and a decrease in pressure in the region of the throat. With a correctly designed venturi the pressure at the throat 

Since there are no moving parts, these feeders are potentially suitable for abrasive and friable materials. Care must be exercised in using venturis to feed such materials into the conveying line, however, for the high air velocity in the throat may lead to considerable erosion and particle degradation in this region. There is no inherent means of flow control and so this means that the venturi would need to be fed from a belt, screw or vibratory feeder. A rotary valve could also be used, since there would be no adverse pressure drop across the valve. 

---

Many diverse devices have been developed for feeding pipelines. Some are specifically appropriate to a single type of system, such as suction nozzles for vacuum systems. Others, such as rotary valves, screws and gate valves, can be used for vacuum and positive pressure systems. The approximate operating pressure ranges for various pipeline feeding devices are illustrated in Figure 4.13. 

Simple systems requiring a prime mover, a feeding device, a conveying pipeline and a cleaning or disengaging device (Marcus et al., 1990). 

Pneumatic conveying systems are basically quite simple and are ideally suited for the transport of powdered and granular materials in factory, site and plant situations. The system requirements are a source of compressed gas, usually air, a feed device, a conveying pipeline and a receiver to disengage the conveyed material and carrier gas. The system is totally enclosed, and if it is required, the system can operate entirely without moving parts coming into contact with the conveyed material. 

Although positive pressure conveying systems discharging to a reception point at atmospheric pressure are probably the most common of all pneumatic conveying systems, the feeding of a material into a pipeline in which there is air at a positive pressure does present a number of problems. A wide range of material feeding devices, however, are available that can be used with this type of system, from venturis and rotary valves to screws and blow tanks. 

The air mover can be positioned at either end of the system shown in Figure 4.12. In positive pressure systems the material has to be fed into the pipeline with air maintained at pressure. As a consequence of this there may be a loss of conveying air across the feeding device. In certain cases this air flow can interfere with the feeding process. In negative... 

When more than one pressure-regulating or compressor station feeds into the pipeline or distribution system and pressure relief devices are installed at such stations, the relieving capacity at the remote station may... 

The product obtained from wells on gas and gas condensate fields is always a complex heterogeneous mixture that contains a mixture of gases (saturated with water vapor and heavy hydrocarbons), liquid hydrocarbons (oil or gas condensate) and water, solid particles of rock, and other components. In order for the gas delivered to the consumer to meet all requirements placed upon it, it is necessary to eliminate the solid and liquid phases and also a part of the water vapor and heavy hydrocarbons before feeding it in the gas-transmission pipeline. These processes are carried out in special field devices of the complex preparation of a gas and condensate (DCPG). The typical design of the DCPG apparatus at a gas-condensate field is shown schematically in Fig. 1.1. The preparation of the gas is carried out by the method of low-temperature separations (LTS). 

Numerous devices have been developed to feed materials into pipelines, as well as to disengage materials from the conveying air at the reception point. In vacuum systems the material feed is invariably at atmospheric pressure and so the pipeline can either be fed directly from a supply hopper or by means of suction nozzles from a storage vessel or stockpile. Pressure capability, control and air leakage are important points to consider... 

---