GB837510A - Multi-stage deaerator with controlled countercurrent steam flow path - Google Patents

Abstract

A method of increasing the hydraulic load in a multi-stage de rator includes the steps of spraying liquid to be de rated into a primary heating and de rating stage; simultaneously delivering steam to the de rator and passing it through at least one other countercurrent flow <PICT:0837510/III/1> <PICT:0837510/III/2> heating and de rating stage in said de rator; collecting and redistributing the fluid from said primary stage and passing it directly to said other heating and de rating stage in countercurrent flow relationship with steam from said other heating and de rating stage, and simultaneously by-passing a portion of said steam directly to the primary stage to control the velocity of the steam passing through said secondary stage, and venting residual steam and non-condensible gases from the de rator. The collected and redistributed fluid may be passed to said other heating and de rating stage through an outlet of relatively greater free cross-sectional flow area than the free crosssectional flow area of said other heating and de rating stage. The method thus includes the step of adjusting the by-passing of steam to maintain a constant pressure loss through said other heating and de rating stage when the differential pressure across the de rator reaches a predetermined maximum either by means of an orifice of predetermined size or by a valve set to open at a certain pressure. Fig. 1 shows one form of a multi-stage de rator comprising an elongated fully enclosed tower 1 having formed therein a water storage section 2, a steam space 3 and a raw water inlet pipe 4 connected to a spring-loaded or orifice-type inlet valve 5 disposed at the upper end of the tower 1 so that water delivered to the tower from the inlet valve 5 will descend by gravity flow to the water storage section. The de rated water in the water storage section 2 is removed from the tower 1 through a water-discharge outlet 10 and an overflow pipe 11 is also provided to prevent the amount of water from rising beyond a predetermined level in tower 1. The steam from any suitable source is admitted to the steam space 3 through a steam inlet 12 which may be disposed medially of the upper portion of the steam space 3. Formed in the steam space 3 are a primary heating and de rating stage generally designated B which is of the spray or jet-type and at least one secondary heating and de rating stage generally designated C of the counter-flow tray or packed-type de rator. The primary stage and secondary stage will be disposed in countercurrent flow relationship so that fluid will be delivered from the primary stage to the secondary stage by gravity flow and steam will pass from the secondary stage upwardly through the primary stage in countercurrent flow. The structure shown in Fig. 4 differs from the structure previously described by the addition of weight load valves 30 connected to the inner wall elongated hollow number 24 which covers the orifices 29, these valves being set to open at a predetermined pressure differential in the tower will obtain the same desired results as in the embodiment of Fig. 1. The effect of this arrangement, that is, proportioning the size of the orifice relative to the area in the lowermost end of the heating and de rating chamber 25, is to control the steam delivered to the primary stage and secondary stage at a relatively constant ratio on the basis of this area relationship, as a result of which the vapour velocity through the second stage of heating and de rating will be limited. This will avoid flooding and permit the apparatus to carry very much higher hydraulic loads than would normally be possible with the conventional counterflow displacement flow path.