Patent Application
20160252307
The present invention relates to a heat exchange system and method, and more particularly to a heat exchange system and method that enables providing a determined heated water temperature at a system heated water outlet and maintaining a substantially constant level of flooding within a flooded heat exchanger.
Flooded heat exchangers are known for use in heat exchange systems such as for heating water, such as in hotels or industrial environments. A flooded heat exchanger comprises a water side and a steam side that are in heat exchange communication with each other, for heating the water with the steam through heat exchange in respective, distinct fluid circuits. As the steam flows through the steam side it condensates to form condensate that flows out of the heat exchanger. The change of phase of the gaseous steam into liquid condensate is highly exothermic and allows the transfer of a significant quantity of energy from the steam to the water to be heated. A valve is installed on the steam side, at the outlet of the heat exchanger, to control the level of condensate being outputted. This allows the level of condensate to be adjusted on the steam side: if the proportion of steam on the steam side is more important, the heat transfer will be more important due to the hotter steam transferring more energy to the water. However, if the condensate is proportionately more important, then the heat transfer will be less important. The variation in the level of condensate on the steam side, is called the level of flooding of the heat exchanger. It is known to calibrate the level of flooding to adjust the heat exchange, to accommodate variations in the demand in hot water on the water side.
These flooded heat exchangers are so-called feedback heat exchangers, in that the temperature at the heated water outlet will be continuously measured to consequently control the control valve to in turn control the level of flooding according to the demand in hot water at the heated water outlet.
One problem with prior art heat exchangers is linked to energy loss related to flash steam at the condensate output line. This energy loss is typically between 3.9% for heat exchangers that operate at 15 psi; to about 6.5% for heat exchangers that operate at 30 psi. The flash steam in the condensate output line is mainly the result of the condensate exiting the heat exchanger at about the saturation temperature. For example, in a heat exchanger that operates at 15 psi, the steam and condensate temperatures are both 250° F., and the energy loss is about 3.9%; while for heat exchangers that operate at 30 psi, the steam and condensate temperatures are both 274° F., and the energy loss is about 6.5%.
The invention pertains to a heat exchange system comprising a system steam inlet, a system condensate outlet, a system cold water inlet, a system heated water outlet, a flooded heat exchanger and a level controller, said flooded heat exchanger comprising:
In one embodiment, said controller steam link is connected to said steam side of said heat exchanger through a heat exchanger steam link, wherein said steam source is said heat exchanger steam side above said condensate level.
In one embodiment, said heat exchange system further comprises a mixer installed between said exchanger heated water outlet and said system heated water outlet, said mixer comprising:
In one embodiment, said controller valve comprises a floater for floating in condensate located in said level controller and a plug connected to said floater and continuously biased towards said controller condensate outlet, said plug sealing said condensate outlet if the level of liquid in said level controller remains below a determined valve activation threshold and clearing said condensate outlet if the level of liquid in said level controller increases beyond said valve activation threshold in which case the liquid will carry said floater and said plug upwardly away from said controller condensate outlet.
The present invention also relates to a method of providing a determined heated water temperature at a system heated water outlet in a heat exchange system, said heat exchange system further comprising a system steam inlet, a system condensate outlet, a system cold water inlet, a system heated water outlet, a flooded heat exchanger, a level controller and a mixer, said flooded heat exchanger comprising an exchanger steam inlet, an exchanger condensate outlet, an exchanger cold water inlet and an exchanger heated water outlet, said method comprising the steps of
In one embodiment, the step of mixing the heated water exiting said flooded heat exchanger with cold water is accomplished with a mixer including a blending valve.
In one embodiment, the step of connecting said level controller to said steam source is accomplished by connecting said steam side of said heat exchanger to said level controller, wherein said steam source is said heat exchanger steam side above said condensate level.
The invention also relates to a method of controlling a level of flooding to remain substantially constant within a flooded heat exchanger, said flooded heat exchanger comprising an exchanger steam inlet, an exchanger condensate outlet, an exchanger cold water inlet and an exchanger heated water outlet, said method comprising the steps of:
In one embodiment, the step of connecting said level controller to said steam source is accomplished by connecting said steam side of said heat exchanger to said level controller, wherein said steam source is said heat exchanger steam side above said condensate level.
The present invention further relates to a method of controlling a level of flooding to remain substantially constant within a flooded heat exchanger wherein steam flows into a steam side and condenses to form condensate that partly floods said steam side and that flows out of said steam side, and wherein cold water flows into a water side in heat exchange relationship with said steam side to heat the cold water and form heated water that flows out of said water side, said method comprising:
In one embodiment, the step of connecting said level controller to said steam source is accomplished by connecting said steam side of said heat exchanger to said level controller, wherein said steam source is said heat exchanger steam side above said condensate level.
In the annexed drawings:
Heat exchange system 10 comprises a system steam inlet 12, a system condensate outlet 14, a system cold water inlet 16, a system heated water outlet 18, a flooded heat exchanger 20, a level controller 22 and a mixer 24.
Flooded heat exchanger 20 comprises an exchanger reservoir 26 in which steam and water can flow in two distinct fluid channels or circuits, namely a steam side 28 and a water side 30 that are distinct fluid circuits without any fluid mixture therebetween; while steam side 28 and water side 30 are in thermally conductive contact with each other to allow heat exchange between each other. Steam side 28 may comprise baffles (not shown) and allows steam to circulate outside of a number of tubes 32 that compose water side and wherein the water to be heated circulates. A single tube 32 is shown in the schematic view of
Heat exchanger 20 comprises an exchanger steam inlet 34 connected to system steam inlet 12 and allowing steam into steam side 28, and an exchanger condensate outlet 36 allowing condensate to exit heat exchanger steam side 28. Heat exchanger 20 further comprises an exchanger cold water inlet 38 connected to system cold water inlet 16 for allowing cold water into the heat exchanger water side 30, and an exchanger heated water outlet 40 connected to system heated water outlet 18 albeit indirectly as detailed hereinafter. Water flowing in water side 30 can consequently be heated by the steam/condensate flowing in steam side 28 through a heat exchange between the water and steam/condensate. Heat exchanger 20, combined to level controller 22, is adapted, by calibrating its size and operational parameters, for allowing a heat exchange that will cause the steam to condensate to thereby partly flood the steam side, causing the condensate to rise at a condensate level 42. Heat exchanger 20 is consequently of the so-called flooded heat exchanger type.
Level controller 22, also shown in
Controller valve 56 comprises a floater 58 for floating in condensate located in level controller 22, a plug 60 connected to floater 58. Plug 60 is continuously biased towards controller condensate outlet 54 by the pressure in level controller 22 such that plug 60 will seal condensate outlet 54 if the level of liquid in level controller 22 falls below a determined valve activation threshold; and will clear condensate outlet 54 if the level of liquid in level controller 22 increases beyond the valve activation threshold. Indeed, in this latter case, the liquid-phase condensate will carry floater 58 and plug 60 upwardly and away from condensate outlet 54.
Level controller 22 also comprises a controller steam link 64 connected to an exchanger steam link 66 that is located on the steam side 28 of heat exchanger 20 and more particularly that is located above the condensate level 42 in heat exchanger steam side 28. Consequently, there is a connection allowing pressure equilibrium between level controller 22 and heat exchanger steam side 28 due to the dual connection that comprises:
This pressure equilibrium, together with the floater 58 and valve 60 assembly, allow the level of condensate in level controller 22 to be controlled to remain substantially constant, due to the controller valve 56 that allows condensate to be selectively exhausted out through controller condensate outlet 54 as a result of the level of condensate within level controller 22 rising beyond said valve activation threshold; while the level of condensate will not be allowed to lower beyond a minimum condensate level that will be the same in heat exchanger 20 and in level controller 22 due to the vertical position of condensate inlet 52 of level controller 22. This control of the level of condensate in level controller 22 consequently concurrently allows the level of flooding in flooded heat exchanger steam side 28 to be controlled to remain substantially constant. Indeed, should the level of condensate 42 in heat exchanger steam side 28 lower, the level of condensate 68 in level controller 22 will also lower due to the pressure equilibrium between the liquid-phase condensate and the gaseous state steam and due to the vertical position of level controller condensate inlet 52, and consequently controller valve 56 will be allowed to lower to block controlled condensate outlet 54 to prevent the level of condensate from further lowering. Conversely, should the level of condensate rise, the condensate will carry floater 58 with it and open condensate outlet 54, allowing condensate to be exhausted. The result is that the level of condensate in heat exchanger steam side 28 will be controlled to remain substantially constant, and by that it is meant that the level of condensate will be controlled to remain between the lowermost level of level controller condensate inlet, as shown by line A in
These operation parameters in heat exchanger 20 allow for the heat exchanger to work in sub-cooling conditions, namely the condensate outlet temperature will be below the saturation level. This avoids the generation of flash steam and consequently completely negates flash steam energy loss. This in turn allows the condensate to be circulated back toward the boiler without use of a pumping station (as normally used in prior art heat exchanger systems) if the differential pressure across level controller 22 is positive.
Positioning the level controller on the condensate outlet of the heat exchanger effectively creates a flooded heat exchanger system, wherein the level of flooding in heat exchanger 20 will be determined at the outset by calibrating the vertical position of level controller 22 relative to the heat exchanger condensate outlet 36 and as a result of the operating parameters of heat exchanger 20, including its size, the pressure/temperature of steam flowing into steam side 28 and the temperature and debit variation of water flowing into and out of water side 30. This is a novel and ingenious way of flooding heat exchanger 20 and specifically allow heat exchanger 20 to work in the above-mentioned advantageous sub-cooling conditions.
It has been found that use of a level controller in a flooded heat exchange system will cost only about $400; while use of a control valve and its accessories in a feedback heat exchange system costs about $4000. This is a further important advantage brought about by the present invention. One reason for this important cost difference is that the level controller is a simple mechanical device that requires no continuous temperature measurement beyond the initial calibration of the heat exchange system, contrarily to the feedback heat exchange system wherein a temperature sensor with associated controls need to be installed for operation of the heat exchange system, to allow control of the condensate outlet valve as a result of measurement of the temperature at the heated water outlet.’
It is noted that controller steam link 64 could be connected to a steam source other than heat exchanger steam side 28. This steam source would need to have a pressure equivalent to that of heat exchanger steam side 28 for the pressure equilibrium to exist between level controller 22 and heat exchanger steam side 28. For example, controller steam link 64 could be connected to system steam inlet 12 upstream of heat exchanger 20.
Mixer 24 is installed between exchanger heated water outlet 40 and system heated water outlet 18—thereby exchanger heated water outlet 40 is said to be connected to system heated water outlet 18, albeit indirectly. Mixer 24 comprises:
Mixer 24, which includes a three-way blending valve 86, could be replaced by any other suitable three-way mixing device such a pneumatic, thermostatic or electric three-way mixing device.
It is noted that although water has been identified herein as the liquid to be circulated on the water side of the heat exchanger, it is understood that any other fluid can be used, for example glycol.
