Patent Application
20140270741
The present invention relates in general to process heaters and in particular to an apparatus, system, and method to control the vessel wall temperature of a process heater.
A process heater is a heater that heats a process fluid, which can be a gas such as methane or air, prior to that process fluid flowing into a subsequent process. An example of a process heater is a heater that heats methane before the methane flows into a power generation furnace. Typical electric process heaters include electric heater elements, or rods, positioned inside a tubular pressure vessel. The process fluid flows through the tubular pressure vessel. Electric current through a filament within the heater element causes the heater element to produce heat, which is transferred to the fluid as the fluid flows past the element. Unfortunately, heat from the heater element is also radiated to the vessel wall. The hot vessel walls can decrease the operational life of the process heater. To overcome the effects of the heat, the vessel wall must be made of a sufficiently thick material and, in some cases, additional insulation is required. Sometimes the vessel must be made of an exotic material to withstand the heat. The thick vessel wall, the choice of material, and the insulation can each increase the cost and the weight of the process heater. It is desirable to transfer heat from the heater elements to the process fluid without inadvertently radiating so much heat to the vessel wall.
An apparatus, system, and method for heating fluidic material includes a sleeve positioned within a housing, and an annulus defined by an exterior surface of the sleeve and an interior surface of the housing. At least a portion of the heating elements pass through the sleeve. As the fluidic material flows through the heater, a portion of the fluidic material flows through the sleeve and a portion of the fluidic material flows through the annulus. A flow restrictor is positioned within the housing to control the flow of fluidic material through the sleeve relative to the flow of fluidic material through the annulus. In embodiments, the fluidic material flowing through the annulus has a higher linear velocity than the flow through the sleeve.
In an embodiment of the apparatus for heating a fluid material, the apparatus includes a tubular housing that defines a passageway, wherein an upstream end of the passageway is adapted to be operably coupled to an inlet stream of fluidic material and a downstream end of the passageway comprises an outlet. A sleeve can be positioned concentrically within the passageway and define an annulus between the sleeve and an inner diameter of the housing, the sleeve having a sleeve passage therethrough, the annulus and the sleeve passage each being in communication with the passageway so that when fluidic materials flow through the passageway, a portion of the fluidic material flow through the annulus and another portion of the fluidic materials flow through the sleeve passage. One or more heating elements can be positioned at least partially within the sleeve and, because the sleeve is within the outer housing, the one or more heater elements are positioned within the outer housing. A flow restrictor can be positioned to control flow through the sleeve relative to the flow through the annulus.
In embodiments, the flow restrictor reduces the flow of fluidic materials through the sleeve passage so that the linear velocity of the fluidic materials in the annulus is greater than the linear velocity of the fluidic materials in the sleeve passage. In embodiments, the flow restrictor includes a cone having a large opening at a first end and a small opening at a second end, the small opening being smaller than the large opening. The cross sectional area of the large opening can be at least two times greater than the cross sectional area of the small opening. In embodiments, the cross sectional area of the large opening is about 1.5 to 5 times greater than the cross sectional area of the small opening. The large opening can be connected to an end of the sleeve and the small opening can be nearer the downstream end of the passageway than the larger opening. The flow restrictor can be nearer the downstream end of the passageway than the sleeve. In embodiments, the fluid flowing through the annulus is turbulent.
In embodiments, the flow restrictor includes a cone having a frustoconical shape, and fluid flowing through the sleeve flows through an interior of the cone and fluid flowing through the annulus flows along an exterior of the cone. In embodiments, the flow restrictor can include a variable flow restrictor, the variable flow restrictor being adapted to change the volume of fluid flow through the sleeve passage in response to conditions within the tubular housing. In embodiments, those conditions within the tubular housing can include a temperature of the tubular housing, a temperature of the fluidic material at the outlet, or the flow rate of the fluidic material.
In embodiments, the cross sectional area of the sleeve passage is about 5-10 times greater than the cross sectional area of the annulus. In embodiments, the cross sectional area of the sleeve passage is at least six times greater than the cross sectional area of the annulus.
In embodiments of a method for heating fluidic material, the method includes the steps of placing a sleeve inside a housing and creating an annulus therebetween; positioning at least one heating element within the housing so that at least a portion of the heating element passes through the sleeve; and flowing a fluidic material through the housing, a portion of the fluidic material flowing through the annulus and a portion of the fluidic material flowing through the sleeve, the portion of fluid flowing through the annulus having a higher linear velocity than the portion of fluid flowing through the sleeve. Embodiments can include the step of the step of positioning a flow restrictor in the housing, the flow restrictor restricting the flow of fluidic material through the sleeve.
Referring to
Housing 102 has an upstream end 110 connected to fluid inlet 112, and a downstream end 114 connected to fluid outlet 116. The fluidic media flows into process heater 100 through inlet 112, is heated as it flows through housing 102 from upstream end 110 toward downstream end 114, and flows out through fluid outlet 116.
Referring to
As best shown in
Referring now to
A power controller 142 supplies power via wires 144 to electrical heater elements 128. A plurality of wires 144 can be used, with each wire 144 being connected to one or more heater elements 128 (for the sake of illustration, only one such wire 144 is shown in
Referring to
Referring to
The portion of fluid flowing through annulus 122 flows past the outer diameter surface of flow restrictor 148 as the fluid flows from the upstream end toward the downstream end of housing 102. In embodiments where flow restrictor 148 has a frustoconical shape and is connected to the downstream end of sleeve 120, the space between the outer diameter of flow restrictor 148 and the inner diameter of housing 102 is a restrictor annulus 154 having a cross sectional area that becomes increasingly larger when moving from the upstream end toward the downstream end. As shown in
In embodiments, flow restrictor 148 can be a variable flow restrictor. A variable flow restrictor can, for example, reduce or increase the size of small opening 152. The variable flow restrictor can change the volume of fluid flow through the sleeve passage in response to conditions within process heater 100. Those conditions can include, for example, the temperature of housing 102, the temperature of the fluidic material at outlet 116, the flow rate of the fluidic material through process heater 100, and the flow ratio sleeve 120 and annulus 122. For example, if the wall of housing 102 becomes too hot, the variable flow restrictor can decrease the flow through the flow restrictor 148 and, thus, increase the velocity of flow through annulus 122. If the heat provided by heater elements 128 is relatively low such that housing 102 remains relatively cool, then the variable flow restrictor can increase the size of small opening 152 to allow a greater percentage of flow through sleeve 120 relative to the flow through annulus 122.
Referring now to
Variable flow restrictor 172 is positioned at an end of sleeve 164. Variable flow restrictor 172 can restrict the flow of fluidic media 170 flowing through sleeve 164 and, thus, cause the fluidic media flowing through annulus 166 to flow at a higher velocity than the fluidic media flowing through sleeve 164. In embodiments, variable flow restrictor can include orifice 174 and plunger 176. In the embodiment shown in
In embodiments, actuator 180 is connected to plunger 176 and can be used to move plunger 176 between the high flow and the low flow positions. Actuator 180 can include, for example, a threaded shaft extending through an end of housing 162. An operator can manually rotate the threaded shaft of actuator 180 to extend and retract plunger 176 relative to orifice 174. In embodiments, actuator 180 can include a controller 182 in communication with, for example, an electric motor, a solenoid, or a piston, that can be used to extend or retract plunger 176. For example, a temperature sensor 184 can send a temperature signal to the controller of actuator 180. In response to the temperature signal, actuator 180 can move plunger 176 to permit more or less flow through orifice 174 and, thus, through sleeve 164. In embodiments, actuator 180 can include a thermal expansion element that expands in response to heat. The thermal expansion element can, for example, begin to expand when the temperature of the thermal expansion unit exceeds a preselected value, and continue to expand in proportion to the temperature. The expansion can cause plunger 176 to move toward the low flow position. When the temperature is reduced, the thermal expansion element can contract, thus causing plunger 176 to move back to the high flow position. One of skill in the art will appreciate that variable flow restrictor 180 is not limited to embodiments of a plunger obstructing an orifice. Other embodiments can be used such as, for example, a damper that variably covers an opening or a cone having movable petals that reduce or enlarge the size of the opening of the cone.
In the event that process heater 160 is running hot, and thus housing 162 is getting hot, variable flow restrictor 172 can reduce the flow through sleeve 164. That reduction can cause increased flow through annulus 166. That increased flow results in more heat being transferred from the exterior of sleeve 164 to the fluidic media in annulus 166 and, thus, reduce the amount of heat transferred from sleeve 164 to housing 162. When process heater 160 is producing less heat, variable flow restrictor 172 can flow more fluidic media through sleeve 164 and, thus, reduce the relative flow through annulus 166.
Referring back to
Another portion of fluidic media 104, identified as fluidic media 104A, flows through annulus 122 between the outer diameter of sleeve 120 and the inner diameter of housing 102. In embodiments, fluidic media 104A can be turbulent as it flows through annulus 122. Such turbulence can facilitate greater heat transfer between the outer diameter of sleeve 120 and fluidic media 104A. Similarly, fluidic media 104B can be turbulent as it flows through sleeve passage 124, which can facilitate greater heat transfer between heater elements 128 and fluidic media 104B. In embodiments, fluidic media 104A flows in parallel to fluidic media 104B, such that fluidic media 104 flows through either sleeve passage 124 or annulus 122, each in the same direction, but no portion of fluidic media 104 flows through both sleeve passage 124 and annulus 122. In embodiments, an insignificant portion of fluidic media 104 may flow through both sleeve passage 124 and annulus 122, but substantially all of fluidic media 104 flows through one or the other, and not both, of sleeve passage 124 and annulus 122. In the embodiment shown in
After flowing past flow restrictor 148, fluidic media 104A merges with fluidic media 104B to form a mixed flow, the mixed flow identified as fluidic media 104C in
Upon mixing, fluidic media 104C has a generally homogenous temperature. The cross sectional area of annulus 122 is substantially smaller than the cross sectional area of sleeve passage 124, so the flow volume of fluidic media 104A, through annulus 122, is substantially smaller than the flow volume of fluidic media 104B, through sleeve passage 124—in spite of the higher flow velocity of fluidic media 104A relative to the flow velocity of fluidic media 104B. Because the flow volume of fluidic media 104A is substantially less than the flow volume of fluidic media 104B, fluidic media 104A does not substantially cool fluidic media 104B when those two fluids mix as fluidic media 104C. Furthermore, because heat from sleeve 120 is transferred to fluidic media 104A and moved downstream, less heat is transferred to housing 102 than would be transferred if fluidic media 104A was not flowing through annulus 122 or if fluidic media 104A had a lower velocity.
Experimental Data
Experiments were conducted using an experimental embodiment of a process flow heater 100. In the embodiment, the housing 102 is 6″ diameter schedule 40 pipe. Twelve u-shaped heater elements 128 are used, thus presenting 24 heating rods within heater 100. Sleeve 120 has an outer diameter of 5.7″ and an inner diameter of 5.5″. The cross sectional area of annulus 122 is 3.4 square inches, and the cross sectional area of sleeve passage 124 is 21.6 square inches. Flow restrictor 148 has a large opening 150 with an inner diameter substantially similar to the inner diameter of sleeve 120, and a small opening 152 having a 2″ diameter. The cross sectional area of large opening 150 is 3.1 square inches and the cross sectional area of small opening 152 is 0.8 square inches.
Experimental data shows that the vessel wall temperature of housing 102 when using the sleeve 120 without the flow restrictor 148 was substantially the same as the vessel wall temperature of housing 102 with no sleeve. A sleeve without a flow restrictor does not significantly reduce the vessel wall temperature during sustained operation. One possible theory for this failure to reduce temperature is that there is insufficient flow in the annulus between the sleeve and the housing to overcome the effect of thermal radiation on the housing. In contrast, using both sleeve 120 and flow restrictor 148 resulted in a 40% temperature reduction at the vessel wall of housing 102.
Experimental data shows a substantial reduction in vessel wall temperature when sleeve 120 and flow restrictor 148 are used. The following Table 1 shows the conditions of the experiments:
The following Table 2 shows the result of the Experiment 1 with and without sleeve 120 (tube).
As illustrated by table 2, the temperature of the internal surface of the outer wall was 586° F. lower when the sleeve and flow restrictor were used. The temperature of the external surface of the outer wall was 629° F. lower when the sleeve and flow restrictor were used. When a smaller outlet size was used (the “Smaller Hole”), the external surface temperature was 1065° F. lower than when no sleeve was used.
The following Table 3 shows the result of the Experiment 1 with and without sleeve 120 (tube).
As illustrated by table 3, the temperature of the internal surface of the outer wall was 569° F. lower when the sleeve and flow restrictor were used. The temperature of the external surface of the outer wall was 748° F. lower when the sleeve and flow restrictor were used.
It is understood that variations may be made in the above without departing from the scope of the invention. While specific embodiments have been shown and described, modifications can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments as described are exemplary only and are not limiting. Many variations and modifications are possible and are within the scope of the invention. Furthermore, one or more aspects of the exemplary embodiments may be omitted or combined with one or more aspects of the other exemplary embodiments. Accordingly, the scope of protection is not limited to the embodiments described, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.
