WO1997013097A1

WO1997013097A1 - Method and device for preventing formation of deposits in pipe systems

Info

Publication number: WO1997013097A1
Application number: PCT/DK1996/000421
Authority: WO
Inventors: Karsten Brink Floor
Original assignee: Fls Automation A/S
Priority date: 1995-10-04
Filing date: 1996-10-04
Publication date: 1997-04-10
Also published as: AU7126496A

Abstract

The invention relates to a method of preventing the deposit formation of gas components condensed by the cooling in a pipe line in which a gas flows that contains condensing components at a high temperature, said pipe line having such length that during transport therein the gases are cooled below the condensing temperature of the alkalis, said gas flow being quenched to a temperature below the condensing temperature of the gas components by a flow of coolant joining the gas flow along the entire circumference of the gas flow. The invention further relates to a device for exercising this method wherein the device comprises a chamber into which a supply line for hot gas debouches, a coolant supply line provided around said gas supply line, the chamber having an increased flow cross section relative to the flow cross sections of the hot gas supply line and the coolant supply line, and wherein an outlet opening for the admixture of hot gas/coolant is provided at a distance from the intlet opening.

Description

Method and device for preventing formation of deposits in pipe systems

The invention relates to a method of preventing the formation of deposits in a pipe line.

In connection with various industrial combustion processes samples of the process gas are taken continuously or at intervals with a view to controlling it and optionally adjusting the process conditions. In cases where such process gas contains components which are deposited on particles in the gas flow and on the pipe walls by cooling of the gas below their condensation temperature, clogging may occur in the pipe system. In case of e.g. cement production there will be a large occurrence of alkalis, fluoride compounds and chloride compounds in such process gas which will form deposits upon cooling. In case of combustion plants it may be lead, zinc, copper and the like.

In connection with the sampling it has so far been common to discharge the amount of flue gas which is not sampled for further analyses to the environment. In that case problems will not arise, of course, with deposits in the pipe system since these pipe systems are comparatively short, and therefore the gas has a comparatively high temperature when discharged. Thus, the condensation of the gas components does not occur until the discharge to the environment has taken place.

However, for environmental reasons it is desirable to convey the gas discharged, a part of which is sampled for further analysis, back to the process plant in order to allow purification of this amount of gas, too, in connection with a usual purification plant for the flue gas. Such reconveyance of the gas means that a considerable length of pipes must be provided therefor. The heat exchange of such pipe with the surroundings will mean that the gas flow in the pipe during the transport in the pipe is cooled below the condensing temperature of the alkalis unless it is possible to maintain the high temperature in connection with the pipe. Such measures are very expensive and the operating costs associated with the supply of energy therefor is also very expensive. For the sake of the mechanical handling of the gas, however, it is desirable and in some instances required to cool the gas.

It is therefore the object of the present invention to provide a method which makes it possible to prevent the formation of deposits on the pipe wall interior in a simple manner.

This object is obtained by a method of preventing the deposit formation of gas components condensed by the cooling in a pipe line in which a gas flows that contains condensing components at a high temperature, said pipe line having such length that during transport therein the gasses are cooled below the condensing temperature of the alkalis, said gas flow being quenched to a temperature below the condensing temperature of the gas components by a flow of coolant joining the gas flow along the entire circumference of the gas flow.

Particularly conveniently a further flow of coolant may join the gas flow, said further flow of coolant being supplied countercurrently to the gas flow. Hereby a quicker and more effective cooling of the hot gas is obtained.

The supply of at least one coolant flow, which is preferably ambient air, along the entire circumference of the hot gas flow ensures that the cooling of the hot gas is effected in free spaces and not on the pipe wall, and thus the alkalis will condense exclusively on the particles present in the gas. The components condensed from the gas will subsequently be reconveyed along with the gas flow to the process plant. Thus, the method according to the invention prevents the cooling and thus the condensing of e.g. the alkalis from occurring on the pipe wall and thus no deposits of such alkalis occur on the pipe wall.

As mentioned, it is preferred that the flow of coolant consists of the ambient air and is present in such an amount as to ensure sufficient cooling and thus condensing of a portion of the components present in the gas influx. The lower limit for the amount of coolant supplied is determined by the gas temperature, the coolant temperature and the heat capacity of the two media and the desired final temperature. Excess coolant will accelerate the cooling rate.

Preferably the flow of coolant is supplied in such a manner that it is oriented towards the interior of the hot gas flow. Hereby turbulence is created in the flow and the admixture and cooling are effected more quickly.

Moreover, the invention relates to a device for exercising the method described in the foregoing.

This device is characterized in comprising a chamber into which a supply line for hot gas debouches, a coolant supply line provided around said gas supply line, the chamber having an increased flow cross section relative to the flow cross sections of the hot gas supply line and the coolant supply line, and wherein an outlet opening for hot gas/coolant is provided at a distance from the inlet opening.

Particularly conveniently a further coolant supply line for countercurrent delivery of coolant relative to the hot gas flow is provided opposite the hot gas supply line. This allows for more quick and efficient cooling of the hot gas, and consequently it is possible to provide the cooling chamber with smaller dimensions. This means a reduction of the production costs as a consequence of the reduced consumption of material, and moreover the ensuing less space-consuming construction will require less space on the installation site.

In order to contribute to a quicker admixture and thus cooling of the hot flue gas by the coolant, the annular coolant supply line is preferably so designed that the coolant flow is oriented towards the interior portion of the hot gas flow. This may be obtained e.g. by providing the coolant supply line in the form of an annular duct with at least one conical side wall.

In order to prevent a cooling of the hot has in the hot gas supply line to a temperature below the condensing temperature of the relevant gas components, an insulating layer is preferably provided between the hot gas supply line and the coolant supply line.

The flow path between inlet and outlet in the device are preferably of such length relative to the amount of hot gas and the amount of coolant that an approximately complete admixture and thus cooling of the flue gas with the coolant has taken place before the outlet opening is reached. The invention will now be described in further detail with reference to an embodiment shown in the drawings. In the drawings:

Figure 1 is a schematical view of a pipe system for taking gas samples from a process, and wherein a device for exercising the method according to the invention is arranged,

Figure 2 is a longitudinal sectional view through a device according to the invention, and

Figure 3 is a cross sectional view through a device according to the invention and along the line A-A shown in Figure 2.

Figure 1 illustrates a pipe system 1 for taking gas samples from a process, wherein said gas contains dust and condensed components. In the pipe system a filter housing 2 is arranged. Through a filter in the filter housing a part of the gas flowing into the pipe system is sampled for analysis in analysis equipment intended therefor. After the filter housing a device 3 according to the invention has been arranged. Herein the hot process gas is cooled below the respective condensing temperatures of the individual gas components by the introduction of cold ambient air. From this device the pipe system conveys the amount of gas not taken to the analysis equipment, back to the process plant where it may be delivered to a purification plant in connection therewith.

Figure 2 illustrates a longitudinal sectional view through the device 3 according to the invention. The hot gas and dust are introduced via a pipe 4 into a chamber 5 consisting of a first and a second end wall 6,7 and a side wall 8 extending between said end walls. The pipe 4 serving to deliver hot flue gas debouches centrally in the first end wall 6. Around the hot gas supply line 4, an annular inlet duct 9 for coolant is provided. By means of an insulating material 10 the flue gas supply line 4 is heat-insulated relative to the coolant supply line 9 in order to prevent cooling of the flue gas within the supply line 4 proper. In the other end wall 7 an inlet 14 for a further coolant flow is provided. The side wall 8 is provided with an outlet 11 for the cool flue gas with a content of gas components condensed on dust particles. The coolant is supplied to the inlet duct 9 via a supply pipe line 12.

The positioning of the inlet 4 and the outlet 11 in the chamber 5 is conditioned by the flue gas not coming into contact with the cold walls prior to cooling of the gas below the condensing temperature of the individual gas components.

It further appears that, on the one side, the annular coolant supply duct 9 consists of the flue gas supply line 4 coated with insulating material 10 and being conically tapering, and on the other side a correspondingly conical side wall 13 is provided in the end wall 6. Owing to the conical side walls, the coolant is conveyed towards the interior of the flue gas influx. Hereby an elevated pressure is created in this area and an ensuing turbulence which enhances the admixture and thus the cooling rate. Simultaneous countercurrent delivery of coolant via the coolant supply line 14 further accelerates the admixture and thus the cooling rate.

In Figure 2, the hot gas flow is indicated by the arrow A. The flow path for the first coolant flow, the presence of which is a prerequisite, is indicated by the arrow B. The further coolant flow supplied countercurrently is indicated by the arrow C. Finally the flow path for the cool gas with its contents of condensed solid components is indicated by the arrow D.

Figure 3 is a cross-sectional illustration of the device in a direction towards the first end wall. The centrally arranged flue gas supply line 4 and the annular coolant supply line 9 are clearly illustrated therein.

The gas flows, i.e. the hot gas flow as well as the coolant flow(s), may conveniently be drawn into the pipe system 1 by means of a single suction draw pump 15 (Figure 1) . However, it will also be an option that the individual supply lines for hot gas and coolant, respectively, to the condensing chamber are provided with pumps that deliver hot gas and coolant, respectively, at superatmospheric pressure. The ratio of the volumes of hot gas to coolant is preferably approximately 1:2. Thus, each coolant supply line delivers one third of the total volume.

Claims

C l a i m s

1. A method of preventing the deposit formation of gas components condensed by the cooling in a pipe line in which a gas flows that contains condensing components at a high temperature, said pipe line having such length that during transport therein the gasses are cooled below the condensing temperature of the alkalis, said gas flow being quenched to a temperature below the condensing temperature of the gas components by a flow of coolant joining the gas flow along the entire circumference of the gas flow, said coolant flow being supplied to the gas flow in the downstream direction.

2. A method according to claim 1, c h a r a c t e r i z e d in that a further coolant flow joins the gas flow, said further coolant flow being supplied countercurrently to the gas flow.

3. A method according to claim 1 or 2, c h a r a c t e r i z e d in that the respective coolant flow consists of ambient air in a sufficient amount to ensure sufficient cooling and thus condensing of the gas influx.

4. A method according to claims 1-3, c h a r a c t e r i z e d in that the downstream coolant flow is directed towards the hot gas flow interior.

5. A device for exercising the method according to claims 1-4, c h a r a c t e r i z e d in comprising a chamber into which a supply line for hot gas debouches, a coolant supply line provided around said gas supply line, the chamber having an increased flow cross section relative to the flow cross sections of the hot gas supply line and the coolant supply line, and wherein an outlet opening for hot gas/coolant is provided at a distance from the inlet opening.

6. A device according to claim 5, c h a r a c t e r i z e d in that a further coolant supply line is provided opposite the hot gas supply line for countercurrent delivery of coolant relative to the hot gas flow.

7. A device according to claim 5 or 6, c h a r a c t e r i z e d in that the annular coolant supply line is so designed that the coolant flow is directed towards the interior of the gas flow.

8. A device according to claim 7, c h a r a c t e r i z e d in that the coolant supply line is an annular duct with at least one conical wall.

9. A device according to claims 5-8, c h a r a c t e r i z e d in that an insulating layer is provided between the hot gas supply line and the coolant supply line thereby preventing a quenching in the hot gas supply line proper.

10. A device according to claims 5-9, c h a r a c t e r i z e d in that the flow path between inlet and outlet has such length relative to the respective amounts of hot gas and coolant that an approximately complete admixture of the flow of flue gas with the coolant has taken place before the outlet opening is reached.