Abstract:
A vent head for a steam system is provided. In one embodiment, the head comprises a body defining a vent head chamber and having a vent head outlet. The vent head comprises a steam inlet conduit having a steam outlet that opens into the vent head chamber and a baffle disposed within the vent head chamber above the steam outlet. A drainage passageway is provided for fluid communication between the vent head chamber and the steam inlet conduit. In use, the steam outlet may discharge steam into the vent head chamber which impinges on the baffle, thereby separating entrained liquid water from the steam. The separated water is collected in the vent head chamber returned to the steam inlet conduit via the drainage passageway.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to GB 1010720.9 filed on 25 Jun. 2010 and GB 1010719.1 filed on 25 Jun. 2010, which are each hereby incorporated by reference in their entirety for any and all purposes. 
     BACKGROUND 
     Aspects of the present invention relates to a vent head for a steam system. 
     In an industrial and heating process utilizing steam, steam is generated in a boiler and transferred through pipework at high temperature and pressure to various industrial processes where the energy in the steam is utilised. 
     Some steam system components, such as blow down vessels, include open-ended steam vent pipes that are used to vent steam to the atmosphere. It is known to provide the steam vent pipes with a vent head in order to safely discharge steam to the atmosphere at a low velocity. 
     One type of known vent head comprises a housing containing a baffle which is arranged to intercept steam entering the housing. The baffle causes water entrained within the steam to be separated from the steam. The dry steam is then vented to the atmosphere through an outlet in the housing and the separated water is fed to a drain line where it is drained from the steam system. 
     Whilst such a vent head is suitable for some applications, there are a number of drawbacks associated with it. For example, it is not capable of separating all of the water that is entrained in the steam. Further, known vent heads can be time consuming to install due to the pipework connections that are necessary. 
     It is therefore desirable to provide an improved vent head that addresses these and other needs. 
     SUMMARY 
     Aspects of the invention relate to vent heads and related methods that improve the separation of entrained water from steam and/or is less complicated to install. According to an aspect of the present invention there is provided a vent head for a steam system, comprising: a body defining a vent head chamber and having a vent head outlet; a steam inlet conduit having a steam outlet that opens into the vent head chamber; a baffle disposed within the vent head chamber and above the steam outlet; and a drainage passageway providing fluid communication between the vent head chamber and the steam inlet conduit; wherein in use the steam outlet discharges steam into the vent head chamber which impinges on the baffle, thereby separating entrained liquid water from the steam, the liquid water being collected in the vent head chamber and returned to the steam inlet conduit via the drainage passageway. 
     The steam inlet conduit may extend into the vent head chamber. The drainage passageway may comprise a hole provided in the portion of the steam inlet conduit which extends into the vent head chamber. There may be a plurality of drainage passageways, each comprising a hole provided in the portion of the steam inlet conduit which extends into the vent head chamber. 
     The body may comprise a bottom wall which slopes downwards towards an inlet of the drainage passageway. 
     The steam inlet conduit may comprise an attachment portion for attaching the steam inlet conduit to an open-ended steam vent pipe. The steam outlet may be arranged such that in use the steam is discharged in a substantially vertical direction. 
     The baffle may be substantially horizontal in use. The baffle may be substantially planar. The baffle may be substantially circular. 
     The body may comprise a top wall within which the vent head outlet is provided. 
     The vent head outlet may be located above the baffle. The baffle may be disposed in the steam flow path between the steam outlet and the vent head outlet. When viewed from above, the baffle may extend beyond the steam outlet. 
     The baffle may comprise an impingement region, on which in use the steam impinges, and a convex portion disposed between the impingement region and the edge of the baffle. The convex portion may have a radius of curvature such that in use water vapour flows around the convex portion to the vent head outlet, and water droplets are discharged from the convex portion into the vent head chamber. The radius of curvature of the convex portion may be between about 4 and about 7 mm. The radius of curvature of the convex portion may be about 5 mm. The convex portion may curve upwardly in the direction away from the impingement region, and terminates at the edge of the baffle. When viewed from above, the convex portion may be located in a position beyond the steam outlet. 
     According to a further aspect of the present invention there is provided a steam system comprising a steam vent pipe having a vent head in accordance with any statement herein. 
     The invention may comprise any combination of the features and/or limitations referred to herein, except combinations of such features as are mutually exclusive. 
    
    
     
       BRIEF DESCRIPTION 
       Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  schematically shows a perspective view of a first embodiment of a vent head; 
         FIG. 2  schematically shows the vent head of  FIG. 1  with a section cut-away; 
         FIG. 3  schematically shows a cross-sectional view of the vent head of  FIG. 1 ; 
         FIG. 4  schematically shows two views of the baffle of the vent head of  FIG. 1 ; 
         FIG. 5  schematically shows an enlarged view of the baffle of the vent head of  FIG. 1 ; and 
         FIG. 6  schematically shows a cross-sectional view of a second embodiment of a vent head. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , the vent head  10  may comprise a body  12  that is provided with a vent head outlet  14 , and a steam inlet pipe (or conduit)  16 . The steam inlet pipe  16  is provided with a flange  18  that can be used to attach the vent head  10  to an open-ended steam vent pipe that supplies steam that is to be discharged, or vented, to the atmosphere. 
     With reference to  FIGS. 2 and 3 , the body  12  of the vent head  10  comprises a top wall  20 , a bottom wall  22 , and an annular side wall  24  and therefore the body  12  is substantially cylindrical. The body  12  is made from a first upper part  12   a  that comprises the top wall  20  and a portion of the annular side wall  24 , and a second lower part  12   b  that comprises the bottom wall  22  and a portion of the annular side wall  24 . The upper and lower parts  12   a ,  12   b  are fitted together to form the body  12 . The body  12  defines a vent head chamber  26  which is the interior of the body  12 . 
     A steam pipe opening  28  is provided in the bottom wall  22  of the lower part  12   b  of the body  12  and a collar  30  axially extends from the opening  28 . The steam pipe opening  28  and the collar  30  are coaxial with the substantially cylindrical body  12 . The steam inlet pipe  16  is located within the opening  28  so that the collar  30  surrounds and is in contact with the outer surface of the steam inlet pipe  16 . The steam inlet pipe  16  is provided with an annular shoulder  29  which the edge of the collar  30  abuts. An upper portion of the steam inlet pipe  16  projects into the vent head chamber  26  and the open end of the upper portion constitutes a steam outlet  15 . A lower portion of the steam inlet pipe  16  extends outside of the body  12  and the open end of the lower portion constitutes a steam inlet  17 . The end of the lower portion of the steam inlet pipe  16  is provided with the flange  18  which allows the vent head  10  to be coupled to the end of a steam outlet pipe (not shown). 
     The steam inlet pipe  16  is provided with four drainage holes  32  that extend through the thickness of the inlet pipe  16 . The drainage holes  32  are level with the bottom wall  22  of the body  12  and are circumferentially spaced from one another by 90°. The bottom wall  22  of the body  12  slopes downwards radially inwardly towards the steam inlet pipe  16  and the drainage holes  32 . The drainage holes  32  provide a drainage passageway between the vent head chamber  26  and the steam inlet pipe  16 . 
     The vent head outlet  14  is provided in the top wall  20  of the upper part  12   a  of the body  12  and is coaxial with the substantially cylindrical body  12 . Therefore, the vent head outlet  14  is above the steam inlet pipe outlet  15 . 
     A baffle  34  is disposed within the vent head chamber  26  and is located above the steam outlet  15  and below the vent head outlet  14 . The baffle  34  is therefore disposed between the steam outlet  15  and the vent head outlet  14 . In this embodiment the baffle  34  is substantially planar and lies in a substantially horizontal plane when in use. The baffle  34  is substantially circular and is coaxial with the cylindrical body  12 . The diameter of the circular baffle  12  is larger than the diameter of the steam outlet  15  and therefore, when viewed from above, the edge of the baffle  34  extend beyond the steam outlet  15 . In this embodiment, the diameter of the circular baffle  34  is approximately the same as the diameter of the vent head outlet  14 . 
     As shown in detail in  FIG. 4 , the baffle  34  comprises a central impingement region  35  and a convex portion  40  which curves upwards. The convex portion  40  is located between the impingement region  35  and the edge of the baffle  34 . In this embodiment the convex portion  40  is the annular edge of the baffle  34  which is curved upwardly. The radius of curvature of the convex portion  40  in this embodiment is approximately 5 mm. However, the radius of curvature may be between 4 and 7 mm in other embodiments. The purpose of the convex portion  40  will be described below. 
     The baffle  34  is provided with three supporting members  36  that are attached to the edge of the baffle  34  and are circumferentially spaced from one another by 120°. The supporting members  36  extend in the axial direction and each supporting member  36  comprises a lip  38  that projects radially outwardly from the end of the supporting member  36 . The supporting members  36  are used to attach the baffle  34  to and support the baffle  34  from the body  12 . As shown in  FIGS. 2 and 3 , the lips  38  of the supporting members  36  engage with the edge of vent head outlet  14  and rest on the top wall  20  of the body  12 , thereby supporting the baffle  34  from the body  12 . 
     In use, the vent head  10  is attached to the open end of a steam vent pipe (not shown) by means of the flange  18 . The steam vent pipe may be the steam vent pipe of any part of a steam system where steam is discharged, or vented, to the atmosphere. Examples include, but are not limited to, the steam vent pipe of a blow-down vessel, a hotwell tank, a feed tank or a pressure-powered pump. 
     Steam is introduced into the vent head  10  through the steam inlet  17  of the steam inlet pipe  16 . The steam is then discharged in a substantially vertical direction into the vent head chamber  26  from the steam outlet  15  of the steam inlet pipe  16 . 
     As shown in  FIG. 5 , the steam exiting the steam outlet  15  impinges on the impingement region  35  of the horizontal baffle  34  which is disposed directly above the steam outlet  15 . As the steam impinges on the baffle  34 , water droplets that are entrained in the steam flow adhere to the surface of the baffle due to surface tension and are therefore separated from the steam flow. Due to the pressure drop between the vent head chamber  26  and the atmosphere, the steam flows towards the vent head outlet  14  and therefore flows radially outwards over the surface of the baffle  34 . The flow of steam over the surface of the baffle  34  drags the water droplets that are adhered to the surface of the baffle  34  by surface tension radially outwards over the surface of the baffle  34  towards the edge of the baffle  34 . 
     As the steam approaches the convex portion  40  of the baffle  34  the water vapour is attracted to the convex portion  40  of the baffle  34  and therefore flows around it and exits the vent head  10  through the vent head outlet. The water vapour flows around the convex portion  40  by virtue of the Coand{hacek over (a)} effect. However, the water droplets adhered to the baffle  34  surface are too heavy to be dragged around the convex portion  40  by the steam flow and therefore are discharged from the convex portion  40 . Since the convex portion  40  is located outside of the steam outlet  15 , these water droplets are collected in the bottom of the vent head chamber  26 . The water separated from the steam by the baffle  34  flows radially inwards along the downwardly sloped bottom wall  22  of the baffle  26  towards the steam inlet pipe  16 . The separated water then flows through the drainage holes (drainage passageway)  32  in the steam inlet pipe  16  into the interior of the pipe  16 . The water is then caused to flow down the internal wall of the steam inlet pipe  16  and is returned to the steam system. 
     The vent head  10  allows the safe discharge of steam to the atmosphere. This is because the baffle  34  slows down the velocity of the steam, and a large proportion of the water droplets entrained within the steam is separated from the steam by the baffle. This results in substantially dry steam being discharged from the vent head outlet. 
     Returning the liquid water separated from the steam to the steam system provides a number of benefits. The water used in the steam system contains various treatment chemicals that help to improve the performance of the system. If water is lost from the system then it is necessary to replenish that water with fresh water which must be treated with these chemicals. Therefore, reducing the amount of water that is lost from the steam system reduces the amount of fresh treatment chemicals that must be added to the system. This provides a cost saving. Further, water lost from the steam system contains useful heat and therefore returning the liquid water separated from the steam by the baffle improves the energy efficiency of the system. 
     A further benefit is that it is not necessary to provide an external drain line connection to the vent head  10  since the separated water is returned to the steam system down the steam inlet pipe  16 . This reduces the amount of pipework and external connections that is required and therefore results in a less expensive and a quicker installation. 
     The convex portion  40  of the baffle  34  extracts (or separated) more liquid water from the steam that can be achieved with conventional baffles. This is at least partly due to the Coand{hacek over (a)} effect which causes the water vapour to be attracted to and flow around the convex portion  40 , whilst forcing water droplets to be discharged into the vent head chamber  26 . The radius of curvature of the convex portion  40  is chosen such that the flow of water vapour across the baffle  34  is attracted to the convex portion  40  and therefore flows around it, whilst water droplets are discharged from the convex portion  40 . 
       FIG. 6  shows a second embodiment of a vent head  10 . This embodiment is similar to the first embodiment except the upper portion of the steam inlet pipe  16  has an increased thickness. Further, the lower portion of the steam inlet pipe  16  is not provided with a flange and is therefore coupled to a steam vent pipe by alternative means.