Pressure Reducing Valve

This valve is use for reduce pressure like from high pressure compressor or high pressure steam from boiler.

• Fully machined forged valve
• Allows controlled start-up and shut-down of different loops in the power plant with a minimum of heat losses
• Resistant against thermal stress and requires no additional preheating above the demand for superheated steam in the inlet
• Cage plug for flow control that results in a protected seat area and high range ability – 50:1 or more Pressure reducing pipes in outlet to create a multistep pressure reduction providing for minimum noise and vibrations
• Special seal bonnet to guarantee tightness and easy maintenance
• Bolted bonnet also used for low pressure class
  

Applications

The BTG valve type VLR has been designed as a pressure reducing valve for high pressure and/or low pressure systems where a steam conditioning valve is not applicable.

The Kv/Cv-value of the valve depends on the pressure ratio p1/p2 and must – for each valve – be calculated in the BTG computer program, where all throttling points in the valve are taken into consideration. Certified dimensional drawing will be supplied by CCI.

Main applications – high pressure system

• Pressure control/turbine bypass.
• Controlled pressure build-up in the boiler.
• Protection against exceeding the design pressure. Note!

However without the safety function for which the valve VLR-O should be used.
Main applications – low pressure system

• Controlled pressure build-up in the reheater.
• Pressure control/bypass of the intermediate and low pressure part of the turbine. This will assist in avoiding release of the safety valves and consequently helps to prevent large condensate losses.
• Protection of the condenser in case of disturbances.
• Turbine extraction control

Main duties – process industry

• Controlled pressure in steam pipes to the process – in parallel with the back pressure turbine.
• Provides the process with steam flow during start-up of the turbine.
• Fast take-over of the whole steam flow from boiler to process when the turbine stops/trips.

Centrifugal Pump With Magnetic Bearing

Magnetic bearing maintain the rotor of a pump in suspension through the force of attraction of a magnetic circuit. Thus although they bear up to weight and hydraulic loads of the impellers and the shaft, they are not really bearings in the traditional sense of the rotating and stationary surfaces bearing on one another. The supporting magnet circuit for each bearing includes stationary magnets in a stator surrounding the shaft, a laminated rotor that on the shaft, and the shaft itself. The stator consists of electromagnet in the traditional heteropolar design, and if a homopolar design is employed, permanent magnets can be added. Sensors monitor the position of the shaft and signal a controller to adjust the magnetic loads to keep the shaft to within about 0.001 in (26 μm) of the desired position.

Magnetic bearings are found in small, high speed turbomachinery such as high speed, multistage, axial flow turbomelecular vacuum pumps. They were introduced into large turbomachinery in the nearly 1980s, mainly in gas compressors and truboexpanders. Their use and acceptance has grown slowly but steady since then. Pump applications of a signings can provide a technically sound bearing with maintenance and operating advantages, including zero wear. However, due to the technical complexity of magnetic bearing systems, the economics of scale associated with production quantities are required to make these systems affordable.

Two representative magnetic bearing equipped pumps are summarize in the table below. One is a multistage boiler feedwater pump and the other a single stage double suction hydrocarbon process pump. The multistage pump was retrofitted with magnetic bearings, together with another identical pump that still contains the oil lubricated bearing, both installed in an electric generating station. The magnetic bearing pump is not encumbered with the usual complexity of a bearing lubrication system.

Parameter	Multistage Pump	Single Stage Pump
Power, hp (MW)	610 (0.46)	800 (0.6)
Rated speed, rpm	3580	1780
Shaft weight, lb (kN)	800 (3.6)	Thrust end: 930 (4.1) Drive end: 1415 (6.3)
Thrust bearing design load, lb (kN)	4000 (17.8)	4000 (17.8)
Number of Stages	8	1

Pump Therminology

Displacement
Discharge of a fluid from a vessel by partially or completely displacing its internal volume with a second fluid or by

mechanical means is the principle upon which a great many fluid transport devices operate. Included in this group are reciprocating piston and diaphragm machines, rotary-vane and gear types, fluid piston compressors, acid eggs, and air lifts.

The large variety of displacement-type fluid-transport devices makes it difficult to list characteristics common to each. However, for most types it is correct to state that (1) they are adaptable to high pressure operation, (2) the flow rate through the pump is variable (auxiliary damping systems may be employed to reduce the magnitude of pressure pulsation and flow variation), (3) mechanical considerations limit maximum throughputs, and (4) the devices are capable of efficient performance at extremely low-volume throughput rates.

Centrifugal Force
Centrifugal force is applied by means of the centrifugal pump or compressor. Though the physical appearance of the many types of centrifugal pumps and compressors varies greatly, the basic function of each is the same, i.e., to produce kinetic energy by the action of centrifugal force and then to convert this energy into pressure by efficiently reducing the velocity of the flowing fluid.

In general, centrifugal fluid-transport devices have these characteristics: discharge is relatively free of pulsation; mechanical design lends itself to high throughputs, capacity limitations are rarely a problem; the devices are capable of efficient performance over a wide range of pressures and capacities even at constant-speed operation; discharge pressure is a function of fluid density; and these are relatively small high-speed devices and less costly.

A device which combines the use of centrifugal force with mechanical impulse to produce an increase in pressure is the axial-flow compressor or pump. In this device the fluid travels roughly parallel to the shaft through a series of alternately rotating and stationary radial blades having airfoil cross sections. The fluid is accelerated in the axial direction by mechanical impulses from the rotating blades; concurrently, a positive-pressure gradient in the radial direction is established in each stage by centrifugal force. The net pressure rise per stage results from both effects.

Electromagnetic Force
When the fluid is an electrical conductor, as is the case with molten metals, it is possible to impress an electromagnetic field around the fluid conduit in such a way that a driving force that will cause flow is created. Such pumps have been developed for the handling of heat-transfer liquids, especially for nuclear reactors.

Transfer of Momentum
Deceleration of one fluid (motivating fluid) in order to transfer its momentum to a second fluid (pumped fluid) is a principle commonly used in the handling of corrosive materials, in pumping from inaccessible depths, or for evacuation. Jets and eductors are in this category.

Absence of moving parts and simplicity of construction have frequently justified the use of jets and eductors. However, they are relatively inefficient devices. When air or steam is the motivating fluid, operating costs may be several times the cost of alternative types of fluid-transport equipment. In addition, environmental considerations in today’s chemical plants often inhibit their use.

Mechanical Impulse
The principle of mechanical impulse when applied to fluids is usually combined with one of the other means of imparting motion. As mentioned earlier, this is the case in axial-flow compressors and pumps. The turbine or regenerative-type pump is another device which functions partially by mechanical impulse.

Measurement of Performance
The amount of useful work that any fluid-transport device performs is the product of (1) the mass rate of fluid flow through it and (2) the total pressure differential measured immediately before and after the device, usually expressed in the height of column of fluid equivalent under adiabatic conditions. The first of these quantities is normally referred to as capacity, and the second is known as head.

Capacity
This quantity is expressed in the following units. In SI units capacity is expressed in cubic meters per hour (m3/h) for both liquids and gases. In U.S. customary units it is expressed in U.S. gallons per minute (gal/min) for liquids and in cubic feet per minute

(ft3/min) for gases. Since all these are volume units, the density or specific gravity must be used for conversion to mass rate of flow. When gases are being handled, capacity must be related to a pressure and a temperature, usually the conditions prevailing at the machine inlet. It is important to note that all heads and other terms in the following equations are expressed in height of column of liquid.