BV 995 Pressure Reducing & Desuperheating Unit

The Fouress Range

Desuperheating is a convenient and efficient method of obtaining steam for process work from a superheated supply.

Superheated steam is passed through a section of pipe into which is fitted one or more spray nozzles depending upon capacity. These inject a fine spray of feed water into the steam which is itself converted into steam, absorbing the heat from the steam and reducing the quantity of superheat. As the water is absorbed the steam supply is augmented.

Fouress offers an unsurpassed range of equipment specially developed to meet all duties from the low capacity 'mini' desuperheater to the BV985 multi nozzle with BV987 pipeline desuperheater. From our principal's range we can also offer the BV 995 steam reducing and desuperheating unit which is capable of handling the massive pressure drops and sonic velocities associated with power generation units.

As a leading manufacturer of automatic control valves, Fouress is able to offer a complete package including the control systems required for efficient desuperheating. The Company's design and application departments are at the service of customers for advice on the selection of systems and equipment to meet specific requirements.

‘Multi-Flow’ Trim

Conditions commonly associated with the service are massive pressure drops in the critical flow category and velocities of the sonic order, with the inevitable result in erosion and excessive noise levels.

To cope with this circumstances the valve trim or flow control element used is of special Blakeborough ‘Multi-Flow’ type, which has proved eminent successful in smooth and safe handling of high energy conditions.

The trim differs radically from the conventional forms in that, instead of the full impact of the pressure drops being taken on a single orifice at the seat, it is broken down into a multiplicity of innocuous sub-divisions.

The essential features is a sleeve or skirt drilled with numerous radial holes, the effect of which is to split the main flow stream into a corresponding number of small volume streams immediately prior to entering the seat bore. The total area of holes exposed to the flow varies according to plug lift, as required by the valve characteristics. On emerging from the holes, the stream converge and impinge together at the center of the seat bore, losing kinetic energy in impact and heat to leave the required balance of pressure energy at the outlet.
 

Balanced Plug

The type of plug generally used is the special ‘Holo’ balanced design. This is of cylindrical form furnished with balancing ports to admit pressure above the plug head, back leakage round the outer periphery being minimised by a piston ring.

Mixer / Silencer Unit

After passing the valve seat, flow enters this stage at acceptable velocity. The cooling water is injected through a number of small holes arranged radially around the circumference, creating a very fine spray which is picked-up in the stream flowstream and carried into the mixer / silencer section.

The holes in the baffle plates of the silencer piece are carefully calculated for each application to create approximately the critical pressure drop value at each section when the unit is passing the maximum flow required.