Practical Process Engineering

👇🏼👇🏼👇🏼👇🏼Some interesting articles regarding DEPRESSURIZATION👇🏼👇🏼👇🏼👇🏼

*Application Annular Venturi desuperheaters reduce steam tempera- ture by bringing superheated steam into direct contact with water. The steam is cooled through the evaporation of the water. These desuperheaters are recommended for use under a wide range of conditions, including steady and variable flows. They can be installed horizontally or vertically up. When installed vertically up, turndown ratio can be increased substantially. *Operation Superheated steam is directed by the cone into the annu- lar area between the cone and pipe wall, increasing both velocity and turbulence. Cooling water is introduced through a narrow slot (or small jets in the 1" and 1 ½" sizes) in the cone at the point of maximum velocity. The combination of velocity and turbulence improves atomiza- tion and produces maximum desuperheater effective- ness. The water pressure required should equal the operating steam pressure. *Performance Annular Venturi desuperheaters are normally used in areas where atomizing steam is not available. Turndown ratio is dependent upon a wide variety of factors, such as installation (horizontal or vertical), amount or residual superheat, and piping. Depending on exact flow condi- tions, units are capable of 20% to 2% flow variation. Pressure drop normally varies between 2 psi and 10 psi.

Annular Venturi Desuperheater

Application Venturi desuperheaters reduce steam temperature by bringing superheated steam into direct contact with water. The steam is cooled through the evaporation of the water. These desuperheaters are recommended for use under a wide range of conditions, including steady and variable flows. They can be installed horizontally or vertically up. When installed vertically up, turndown ratios can be increased substantially. Operation Water entering the desuperheaters is preheated in the circulatory chamber around the water diffuser tube and is introduced in many small jets to assist final atomization by the steam flow through the center of the throat. When leaving the throat, the mixture of steam and water enters the venturi section for turbulent mixing prior to entering the main steam line in a fog-like condition without contacting the sidewalls - providing maximum desuperheating effectiveness and a minimum of wear in the discharge piping. The water pressure required should equal the operating steam pressure. Performance Venturi desuperheaters are normally used in areas where atomizing steam is not available. Turndown ratio is dependent upon a wide variety of factors, such as installation (horizontal or vertical), amount of residual superheat, and piping. Depending on exact flow conditions, units are capable of 50% to 5% flow variation. Pressure drop varies between 2 psi and 10 psi.

Venturi desuperheaters

Performance These units employ one or more special spray nozzles to atomize the water droplets and produce the heat transfer contact area necessary for cooling the steam and evaporating the droplets. Because droplets are relatively coarse and the steam temperature entering the unit is normally above 800ºF, it recommends and supplies a thermal sleeve welded to the unit which extends approximately 1 foot downstream in the customer's piping. Water pressure to this type unit differs from all other types in that it is required at a minimum of 25 psi above line pressure. ApplicAtion The mechanical atomizing type desuperheater was developed for economically desuperheating high steam flows in large steam lines, i.e. 20", 24", 30", 36", etc. Initial applications were for periodic usage on emergency dump to condenser systems in power stations where precise desuperheating was not necessary and excess water flows were common. These units are also used on controlled over-pressure dump and bypass systems. construction It consists of only three basic components: body, spray shield, and nozzle assembly. Bodies are normally cast carbon, alloy or stainless steel with weld ends. Stainless steel nozzles are removable from body nozzle bosses. Spray shield is stainless steel pipe or rolled plate. See reverse side for control schematic.

Mechanical Atomizing Dump Desuperheater

OperATiON Water, entering as indicated, flows on a splash plate and is distributed over a perforated plate in the top of the basket containing the reaction rings. The water flows over these metal rings, wetting them thoroughly and providing ample surface for contacting the steam. The high temperature steam flows through the reaction ring section and is desuperheated by contacting the wetted rings. It flows out through the plate at the bottom of the basket and passes through a water deflector and separator into the desuperheater outlet. Excess water drains to the bottom and should be removed through a trap. ApplicATiON The surface absorption type unit is generally used where space limitations and requirements of minimum water carryover are stipulated. Normally used in the marine, food processing and drying industries. Units have been in operation for over 40 years with minimum service required. See reverse side for control schematic.

Surface Absorption Desuperheater

OPERATION Ejector-type steam atomizing desuperheaters utilize steam at higher than line pressure to atomize water. In the Type 6970, the ejector action is used to entrain condensate from the pipeline. This is an important S&K innovation and a feature of this type unit. Few problems are encountered in operating desuperheaters at normal pipeline velocities. However, S&K research has proved conclusively that at low pipeline velocities encountered at 1/50 up to 1/4 of normal flow, unvaporized liquid will “settle out” of a horizontal stream. When it is desired to approach saturation temperature within 10°F, it becomes impossible to completely vaporize the liquid. Thus, while superheated steam is flowing through the pipeline, water accumulates in the bottom of the line. Since this keeps temperature from being reached, a control valve will continue to supply or “pump” excess water into the line while attempting to maintain the control temperature. They overcomes these complications by recycling excess water back into the atomizing device. The water added through the control valve is therefore limited to the amount required for desuperheating. As indicated in in above pictures, high pressure steam enters through the ejector steam nozzle which is precisely designed for each application. This steam entrains the mixture of fresh and excess cooling water through the water inlet line and atomizes this water, which is discharged into the superheated steam line at saturation temperature. The preheating reduces the time required to evaporate the liquid, and the consequent small particle size and turbulent stream improves heat transfer. At low flows the return line entrains excess water. At high flows, where no excess water is required, the unit operates as a steam atomizing desuperheater.

Steam Ejector, Atomizing Desuperheater

*Annular_Venturi_Orrifice_Desuperheater *Application Annular Venturi Orifice Desuperheaters desuperheat steam by bringing it into direct contact with cooling water at a restricted point in the pipeline where high turbulence is created. These units have no moving parts of any kind and pressure drop is low. Steam can be desuperheated down to 10°F. above saturation over an amazing range of flow varying from 100% down to 2% of rated capacity - a 50 to 1 turndown. This high turndown ratio is accomplished at water pressures no higher than the pressure of main steam flow entering the desuperheater. No auxiliary source of high pressure steam is required. *Operation Desuperheaters of this type have an elongated annular insert which forces the steam to flow around it. Midway up the insert at the point of greatest restriction, there is an annular orifice. Cooling water is injected, making contact with the steam at the point of greatest turbulence. Steam and water are thus thoroughly mixed. There is even distribution of the water throughout the stream of steam, and the contact between steam and water is maintained over a long enough period to completely vaporize the water. Annular Venturi Orifice Desuperheater design overcomes the most common problem of desuperheating - the accumulation of unvaporized water in the pipeline. This efficiency-destroying phenomenon cannot happen in this Desuperheater because any water droplet that fails to vaporize immediately after injection must fall back into the high-velocity throat region of the desuperheater where is comes into contact with the steam again and again until it is completely vaporized.