GB1579325A - Blowdown tanks for boller installations - Google Patents

Description

(54) IMPROVEMENTS RELATING TO BLOWDOWN TANKS FOR BOILER INSTALLATIONS (71) We, CURWEN & NEWBERY LIMITED, of Westecroft House, Alfred Street, Westbury, Wiltshire, a British Company, do hereby declare the invention, for which I pray that a Patent may be granted to me, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to blowdown tanks for boiler installations.

Steam boilers accumulate solid matter from the feed water and this has to be removed, intermittently or in a continuous process. This is done by employing blowdown tanks, which receive the contaminated water and allow it to cool before being discharged to a drain. Direct discharge of hot water from a boiler to a drain is generally not permitted. Any solids settling out in the tank can readily be removed at intervals.

This wastes heat, for hot water is being discharged and thrown away. However, because the water is highly contaminated there are difficulties in using it or the flash steam that is generated by its discharge into a blowdown tank.

It is an object of this invention to enable some of this heat to be recovered.

According to the present invention there is provided a blowdown tank having a chamber providing a zone separated from the inlet by an impermeable barrier above the normal water level, but to which there is access below said level there being an outlet from said zone for escape of flash steam emanating from the surface of water in said zone.

Thus the blowdown water cannot discharge directly into the flash steam recovery zone, and that steam is therefore substantially free of contaminants.

For a better understanding of the invention some constructional forms will now be described, by way of example, with reference to the accompanying drawings, in which: Figures 1 to 11 are all sectional elevations of blowdown tanks, and Figure 12 is a diagram of a boiler installation with a blowdown tank.

The blowdown tank of Figure 1 is a generally cylindrical vessel with domed ends and its axis vertical. It has an inlet 2 to which a boiler is connected through valves (not shown), and an outlet 3 which commences internally of the tank in a downwardly extending pipe 4 open at its lower end near the bottom of the tank. The pipe 4 is equipped at its upper end with a vacuum breaker 5 to prevent syphoning. At the lowermost point of the tank there is a drain outlet 6 through which solid effluent is removed, and at the uppermost point there is a vent 7. These features are common to most of the other embodiments to be described and will be similarly referenced in the remaining Figures.

A large diameter tube or cylinder 8, open at its lower end and with further openings 9 near that lower end extends vertically upwards within the tank to emerge through the upper domed end. It is spaced from the inner cylindrical wall of the tank 1. Above the domed upper end, it is coupled to a further conduit 10 which carries away the flash steam liberated from the surface of the water within the pipe 8. This occurs whenever the boiler blowdown water is admitted to the inlet 2. In order to assist this action by back-up pressure, the vent 7 will normally be closed, as by a water seal or a safety valve (not shown).

The normal water level will be above the openings 9 and slightly below outlet 3. The blowdown water is highly contaminated with solids and when it enters the tanks there is considerable agitation, coupled with a reduction in pressure compared with that in the boiler. A certain amount of flash steam is released immediately, and that which is in direct contact with the blowdown water, outside the tube 8, will consequently be contaminated. However within the tube 8, which acts as a separator and steam collector, more stable conditions prevail, for the blowdown water does not have ready access. Therefore the flash steam released there does not carry over contaminants to the conduit 10.

Figure 2 shows a modified flash steam col lector which covers, relatively, a much larger area. It is in the form of a bell-shaped vessel 11 whose lower end is designed normally to be below the ideal water level in the tank. The upper end is connected to a short pipe 12 that emerges centrally at the domed upper end of the tank 1 to be coupled to conduit 10. The vent 7, fitted with safety valve 13, is positioned off-centre of the top of the tank. The inlet 2 enters the tank almost tangentially and the inside wall is protected by a stainless steel plate 14. A gauge glass 15 is provided;it is optional for this and all other embodiments. It will be appreciated that with the greater surface area of water exposed within the vessel 11 there will be correspondingly more flash steam recovery.

In figure 3 the blowdown tank 1 is partitioned towards its upper end by a horizontal plate 16 which supports a co-axial open ended tube 17. This extends down towards the lower end of the tank and also a short distance above the plate 16. Flash steam from the surface of the water within tube 17 will escape through outlet 10 at the top of the tank. Condensate in the chamber above the plate 16 is carried away through drain 16'.

In Figure 4, the blowdown water is first directed into a header tank 18 and then it falls through co-axial tube 19 into the main tank 1, where the normal water level is above the bottom of the tube. Flash steam from the annular surface surrounding the tube 19 escapes through the outlet 10 near the top of the tank.

Figure 5 is a modification of Figure 4, the header tank and the tube being combined into one large diameter cylinder 20, closed at its upper end and its lower end being open below the normal water level.

Figure 6 shows an arrangement where the flash steam is not removed from the vessel which first receives the blowdown water. This is directed through inlet 2 into a first tank 21 which is connected to a second tank 22 through a large diameter conduit 23 between their lower ends. The second tank serves as the flash steam heat recovery vessel, being provided with central upper outlet 10. The water level in both tanks will be the same and the final outlet 3 for water is also from the second tank.

Figure 7 is a modification of Figure 5, in that the blowdown water is directed into a central tube 24 open near the bottom of the main tank 25. However, above this level the tank has a wider section 26 and at the side of this there is the water outlet 3.The normal water level is in the wider section, and consequently presents a large surface area. This increases the flash steam available, and it is recovered from outlet 10 in the upper face of the wide section 26.

The tube 24 converges towards its open lower end, and this reduction of cross-sectional area at the entry for water reduces the carryover of contaminants. Other embodiments may have similarly restrictive entries to the flash steam chamber.

Figure 8 shows a blowdown tank that is suitable for recovering flash steam when there is continuous blowdown. In many respects it is similar to Figure 2, but the tank 1 is made in two sections, 27, 28 removably jointed together by a flange coupling. The top section 28 has an inlet 2 and can readily be removed for inspection, cleaning and repair. There is shown here a pressure gauge 29 for measuring the recovered flash steam.

Figure 9 is effectively Figures 1 and 8 combined, and so adapted that flash steam can be recovered from continuous or intermittent blowdown. Thus the Figure 8 assembly replaces the tube 8 of Figure 1 and there are two inlets available, the inlet 2 to the main tank being for intermittent blowdown and the inlet 2 being for continuous blowdown.

Figure 10 is a development of Figure 9 in that it is designed to cope with continuous and intermittent blowdown. A tube 30 extends vertically through top and bottom of the tank. It is apertured within the tank, below normal water level, and has an inlet 2' for continuous blowdown. This embodiment can be adapted for indirect heat recovery, as illustrated in Figure 12, with a heat exchange element inserted in the tube 30 and fitted by the flange connection at the lower end.

In Figure 11, a blowdown tank is made up of sections. These are cylindrical members 31, 32, 33 outwardly flanged at their ends, and bolted and sealed together. The upper one 31 is the flash recovery section, the middle one 32 is that to which blowdown water is directed via the inlet 2, and which has outlet 3, and the lower one 33 includes an indirect heat recovery device such as a coiled tube 34 which forms a heat transfer element between the blowdown tank water and fluid in the tube. At the lower end of this section there is the usual drain 6.

Figure 12 shows a complete boiler blowdown system in which the boiler 38 is fed with water from a tank 36 via a pump 37. The water for replenishing the tank is supplied from a cold water source (not shown) and is passed through the heat exchanger provided by the blowdown tank, in the Figure 10 or Figure 11 form for example. Thus the boiler feed water is pre-heated. The blowdown connection between the bottom of the boiler and the blowdown tank is indicated at 38.

In several of the above described embodi- ments where there is a relatively small flash steam tube compared with the tank, such as Figures 1,3,8,9 and 10, the design may be modified by providing two or more such tubes in parallel, partially immersed in a common bath of blowdown water.

WHAT WE CLAIM IS: 1. A blowdown tank having a chamber providing a zone separated from the inlet by an impermeable barrier above normal water level but to which there is access below said level, there being an outlet from said zone for escape

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (19)

**WARNING** start of CLMS field may overlap end of DESC **. lector which covers, relatively, a much larger area. It is in the form of a bell-shaped vessel 11 whose lower end is designed normally to be below the ideal water level in the tank. The upper end is connected to a short pipe 12 that emerges centrally at the domed upper end of the tank 1 to be coupled to conduit 10. The vent 7, fitted with safety valve 13, is positioned off-centre of the top of the tank. The inlet 2 enters the tank almost tangentially and the inside wall is protected by a stainless steel plate 14. A gauge glass 15 is provided;it is optional for this and all other embodiments. It will be appreciated that with the greater surface area of water exposed within the vessel 11 there will be correspondingly more flash steam recovery. In figure 3 the blowdown tank 1 is partitioned towards its upper end by a horizontal plate 16 which supports a co-axial open ended tube 17. This extends down towards the lower end of the tank and also a short distance above the plate 16. Flash steam from the surface of the water within tube 17 will escape through outlet 10 at the top of the tank. Condensate in the chamber above the plate 16 is carried away through drain 16'. In Figure 4, the blowdown water is first directed into a header tank 18 and then it falls through co-axial tube 19 into the main tank 1, where the normal water level is above the bottom of the tube. Flash steam from the annular surface surrounding the tube 19 escapes through the outlet 10 near the top of the tank. Figure 5 is a modification of Figure 4, the header tank and the tube being combined into one large diameter cylinder 20, closed at its upper end and its lower end being open below the normal water level. Figure 6 shows an arrangement where the flash steam is not removed from the vessel which first receives the blowdown water. This is directed through inlet 2 into a first tank 21 which is connected to a second tank 22 through a large diameter conduit 23 between their lower ends. The second tank serves as the flash steam heat recovery vessel, being provided with central upper outlet 10. The water level in both tanks will be the same and the final outlet 3 for water is also from the second tank. Figure 7 is a modification of Figure 5, in that the blowdown water is directed into a central tube 24 open near the bottom of the main tank 25. However, above this level the tank has a wider section 26 and at the side of this there is the water outlet 3.The normal water level is in the wider section, and consequently presents a large surface area. This increases the flash steam available, and it is recovered from outlet 10 in the upper face of the wide section 26. The tube 24 converges towards its open lower end, and this reduction of cross-sectional area at the entry for water reduces the carryover of contaminants. Other embodiments may have similarly restrictive entries to the flash steam chamber. Figure 8 shows a blowdown tank that is suitable for recovering flash steam when there is continuous blowdown. In many respects it is similar to Figure 2, but the tank 1 is made in two sections, 27, 28 removably jointed together by a flange coupling. The top section 28 has an inlet 2 and can readily be removed for inspection, cleaning and repair. There is shown here a pressure gauge 29 for measuring the recovered flash steam. Figure 9 is effectively Figures 1 and 8 combined, and so adapted that flash steam can be recovered from continuous or intermittent blowdown. Thus the Figure 8 assembly replaces the tube 8 of Figure 1 and there are two inlets available, the inlet 2 to the main tank being for intermittent blowdown and the inlet 2 being for continuous blowdown. Figure 10 is a development of Figure 9 in that it is designed to cope with continuous and intermittent blowdown. A tube 30 extends vertically through top and bottom of the tank. It is apertured within the tank, below normal water level, and has an inlet 2' for continuous blowdown. This embodiment can be adapted for indirect heat recovery, as illustrated in Figure 12, with a heat exchange element inserted in the tube 30 and fitted by the flange connection at the lower end. In Figure 11, a blowdown tank is made up of sections. These are cylindrical members 31, 32, 33 outwardly flanged at their ends, and bolted and sealed together. The upper one 31 is the flash recovery section, the middle one 32 is that to which blowdown water is directed via the inlet 2, and which has outlet 3, and the lower one 33 includes an indirect heat recovery device such as a coiled tube 34 which forms a heat transfer element between the blowdown tank water and fluid in the tube. At the lower end of this section there is the usual drain 6. Figure 12 shows a complete boiler blowdown system in which the boiler 38 is fed with water from a tank 36 via a pump 37. The water for replenishing the tank is supplied from a cold water source (not shown) and is passed through the heat exchanger provided by the blowdown tank, in the Figure 10 or Figure 11 form for example. Thus the boiler feed water is pre-heated. The blowdown connection between the bottom of the boiler and the blowdown tank is indicated at 38. In several of the above described embodi- ments where there is a relatively small flash steam tube compared with the tank, such as Figures 1,3,8,9 and 10, the design may be modified by providing two or more such tubes in parallel, partially immersed in a common bath of blowdown water. WHAT WE CLAIM IS:

1. A blowdown tank having a chamber providing a zone separated from the inlet by an impermeable barrier above normal water level but to which there is access below said level, there being an outlet from said zone for escape

of flash steam emanating from the surface of water in said zone.

2. A blowdown tank as claimed in claim 1, wherein said impermeable barrier is an upright tube or cylinder.

3. A blowdown tank as claimed in claim 2, wherein the inlet is to the exterior of said tube and the steam outlet is at the upper end of said tube.

4. A blowdown tank as claimed in claim 3, wherein the tank is in at least two separable portions, one above the other.

5. A blowdown tank as claimed in claim 4, wherein there are two said portions, the upper one having said inlet.

6. A blowdown tank as claimed in claim 4, wherein there are three said portions, the central one having said inlet.

7. A blowdown tank as claimed in claim 2, wherein the inlet communicates with the interior of said tube and the steam outlet is from the space within the tank surrounding said tube.

8. A blowdown tank as claimed in claim 7, wherein the tank has a larger horizontal crosssectional area at the normal water level than at other points below said level.

9. A blowdown tank as claimed in claim 1, wherein said tank comprises two vessels joined by a conduit at their lower ends, the inlet being to one vessel and the steam outlet being from the other vessel.

10. A blowdown tank as claimed in claim 2 or 3, wherein there are two inlets, one to said tank and another to a chamber extending into said tank and open to receive blowdown water from within the tank as well as from said other inlet, said tube or cylinder being within said chamber.

11. A blowdown tank as claimed in claim 10, wherein said chamber extends generally vertically through the tank and is apertured within the tank for the passage of blowdown water.

12. A blowdown tank as claimed in any preceding claim, wherein a heat exchange element is fitted to transfer heat from blowdown water in said tank to another fluid passed through said element without direct contact with the blowdown water.

13. A blowdown tank as claimed in claims 6 and 12, wherein said heat exchange element is fitted to the lower of the three tank portions.

14. A blowdown tank as claimed in claims 11 and 12, wherein said heat exchange element is fitted to the lower end of said chamber.

15. A blowdown tank substantially as hereinbefore described with references to the accompanying drawings.

16. A blowdown tank as claimed in any preceding claim, wherein the portion of the tank to which the inlet has direct access is closed by a safety valve and/or water seal.

17. A blowdown tank as claimed in any preceding claim, wherein the access to said zone is restricted compared with the surface from which flash steam emanates.

18. A blowdown tank as claimed in any preceding claim, wherein there is a plurality of said barriers and zones.

19. A method of recovering heat from contaminated hot waste water, wherein the water is directed to a blowdown tank as claimed in any preceding claim and flash steam is recovered from the outlet of said zone.