Throttling process

TABLE 2. Energy consumption of a compressor process. Throttling to the subciitical state. Supercritical solvent CO2. Conditions of the extraction 40 MPa. 313 K Conditions of the regeneration 5 MPa, 299 K. 

TABLE 3. Energy consumption of solvent CO2. a compressor process. Throttling in the supercritical state. Supercritical ... 

If high wellhead pressures are available over long periods, cooling can be achieved by expanding gas through a valve, a process known as Joule Thomson (JT) throttling. The valve is normally used in combination with a liquid gas separator and a heat exchanger, and inhibition measures must be taken to avoid hydrate formation. The whole process is often termed low temperature separation (LTS). 

Variable Air Flow Fans. Variable air flow fans are needed ia the process iadustry for steam or vapor condensing or other temperature critical duties. These also produce significant power saviags. Variable air flow is accompHshed by (/) variable speed motors (most commonly variable frequency drives (VFDs) (2) variable pitch fan hubs (J) two-speed motors (4) selectively turning off fans ia multiple fan iastaHations or (5) variable exit louvers or dampers. Of these methods, VFDs and variable pitch fans are the most efficient. Variable louvers, which throttle the airflow, are the least efficient. The various means of controlling air flow are summarized ia Table 3. 

FIG. 8-85 Pressure, flow, and power for a throttling process using (1) a control valve and a constant speed pump and (2) an adjustable speed pump. 

Change process to adjust specific gravity to design value, or throttle pump to reduce horsepower requirements. This will not correct problem with some vertical turbine pumps that have a flat horsepower-required curve. 

Throttle bushings (Fig. 10-117) are commonly used with single internal or external seals when sohds are present in the fluid and the inflow of a flushing fluid is not objectionable. These close-clearance bushings are intended to serve as flow restric tions through which the maintenance of a small inward flow of flushing fluid prevents the entrance of a process fluid into the stuffing box. 

Process Controls If the inlet or outlet liquid to a piuTro-tnrbiue is regulated by a level controller on the hqnid-snpply vessel, a falling liquid level inside the vessel will cause this coutroUer to throttle a valve, reducing the differential pressure available to the pump-... 

In an industry there may be many drives that may not be required to operate at their optimum capacity at all times. The process requirement may require a varying utilization of the capticity of the drive at different times. In an induction motor, which is a constant speed prime-mover, such a variation is conventionally achieved by throttling the How valves or by employing dampers. 

The rated discharge is at a static head of /7j and a motor h.p. P. In the process of controlling the discharge from Q to and Qy, the valve is throttled, which increases the head loss of the system (or system resistance) from A/ji to and H,yy respectively. The operating point on the curve now shifts from point A[ to /It... 

Startup flow to the expander is designed to be supplied from the discharge of the compressor through a throttle valve and cooler. A careful study of the characteristics of the compressor blow-off valve and the expander startup valve was performed by Solvay process engineers. Based on these calculations, the startup cooler and valve were sized to supply the minimum required flow to tlie expander wheel. 

For the purpose of this chapter, instrumentation will be considered everything from the primary element monitoring the controlled variable through the control valve performing the throttling action. The process equipment interacts with the instrumentation to provide the process... 

Process steam can be supplied at two or more pressures without having to purchase boilers operating at different pressures or having to throttle steam, which is a waste of useful energy. 

A process pressure increase over a set value would cause a signal to reach the suction throttle valve and would close the valve in order to reduce the inlet pressure. 

Figure 6-32 illustrates ejector systems with large condensable loads which can be at least partially handled in the precondenser. Controls are used to maintain constant suction pressure at varying loads (air bleed), or to reduce the required cooling water at low process loads or low water temperatures [2]. The cooler W ater must not be throttled below the minimum (usually 30%-50% of maximum) for proper contact in the condenser. It may be controlled by tailwater temperature, or by the absolute pressure. 

Where extraction turbines are employed, it is most efficient to operate at the lowest level of condensing possible (the highest level of extraction). This occurs when steam from the turbine is extracted and directed by various takeoffs, either to air or water heaters or to industrial processes requiring steam. This practice occurs because no heat is lost from the steam flowing from the throttle to the extraction takeoff (whence it can be delivered for beneficial use by the industrial process), whereas over two-thirds of the heat flowing from the throttle to the surface condenser is ultimately rejected, so efficiency suffers. 

Gas expanders for power recovery may be justified at capacities of several hundred FIP otherwise any needed pressure reduction in process is effected with throttling valves. 

Figure 5.2. Two of the more common types of low pressure CVD reactor, (a) Hot Filament Reactor - these utilise a continually pumped vacuum chamber, while process gases are metered in at carefully controlled rates (typically a total flow rate of a few hundred cubic centimetres per minute). Throttle valves maintain the pressure in the chamber at typically 20-30 torr, while a heater is used to bring the substrate up to a temperature of 700-900°C. The substrate to be coated - e.g. a piece of silicon or molybdenum - sits on the heater, a few millimetres beneath a tungsten filament, which is electrically heated to temperatures in excess of 2200 °C. (b) Microwave Plasma Reactor - in these systems, microwave power is coupled into the process gases via an antenna pointing into the chamber. The size of the chamber is altered by a sliding barrier to achieve maximum microwave power transfer, which results in a ball of hot, ionised gas (a plasma ball) sitting on top of the heated substrate, onto which the diamond film is deposited.

Low contamination levels are readily achieved in laboratory scale UHV systems. Very high costs inhibit the use of UHV in industrial scale systems, however, so another, local-UHV approach has been proposed, viz. the plasma box reactor [152]. The substrate is mounted in a box, which is surrounded by a shell, which is pumped to a low pressure. The process pressure in the box is maintained by a throttle valve. As the pressure in the box is larger than the pressure in the surrounding shell, contaminants diffuse outwards and the incorporation of contaminants in the deposited layer is low. 

Adapa, S., Schmidt, K. A., and Toledo, R. (1997). Functional properties of skim milk processed with continuous high pressure throttling. /. Dairy Set. 80,1941-1948. 

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