EP3027996B1

EP3027996B1 - Fired heat exchanger pipe

Info

Publication number: EP3027996B1
Application number: EP14761710.4A
Authority: EP
Inventors: Krzysztof SZCZEPANSKI; Bartlomiej KOSINSKI
Original assignee: AIC SA
Current assignee: AIC SA
Priority date: 2013-08-02
Filing date: 2014-07-30
Publication date: 2017-07-19
Anticipated expiration: 2034-07-30
Also published as: WO2015016726A1; PL404969A1; ES2642538T3; EP3027996A1; PL223582B1

Description

The invention concerns a pipe for a fired heat exchanger, designed particularly for exchangers fitted with a combustion chamber, where the combustion gases are discharged from the combustion chamber via pipes running through the heat exchange chamber filled with the flowing agent to be heated, water in particular.
Known are many types of pipe systems intended for heat exchangers, where the shapes of the pipes differ depending on their intended location, heat-exchanging agents circulating therein, and individual requirements and needs.
Known from the European patent application EP2384837 is a heat exchanger pipe, a fragment of which is non-circular - preferably rectangular - in cross-section. The pipe is corrugated lengthwise and/or crosswise.
Known form patent application published under No. EP2149779 is a pipe system placed inside a cylindrical casing of the heat exchanger, where the cross-section of each pipe is not identical along the whole length, i.e. the pipe is flattened in the centre and both its ends are circular in cross-section.
Known from European patent application published under No. EP1429085 is a heat exchanger with a number of pipes placed inside the heat exchange chamber between the front and back plates. Each pipe for the exchange of heat between two agents is partially deformed, i.e. there are fragments along the length of each pipe deformed so as to achieve cross-sections other than circular. The pipes are adjacent on one another with contact points between the pipes in specifically selected locations. A pipe according to the preamble of claim 1 is known from US 2011/0146594 A1 The heat exchanger pipe according to the invention is disclosed in claim 1. The wave lengths and amplitudes, as well as the distance between the essentially parallel walls in the corrugated flattened central part of the pipe change along its length.
Preferably, the wave length and amplitude in the corrugated flattened central part of the pipe, and the distance between the essentially parallel pipe walls decrease smoothly along the pipe length.
There are lengthwise grooves along the opposite walls of the corrugated flattened central part of the pipe, which form inward ribs.
In preferable pipe embodiment there are two ribs on each of the opposite walls of the corrugated flattened central part, forming two opposite pairs of ribs.
In particularly preferable pipe embodiment the diameter of the cylindrical ends of the pipe is lesser than 50 mm, and the thickness of the walls does not exceed 1 mm.
The major advantage of the solution according to the invention consists in that it substantially improves the strength parameters of the pipe in the area where the shape of its cross-section changes.
An exemplary embodiment of the pipe of fired heat exchanger, according to the invention is illustrated on the drawing, where Fig. 1 shows the cross-section of a pipe fragment on the side of the first end, Fig. 2 presents the view of the pipe fragment from the side of the first end, Fig. 3 depicts the cross-section of the pipe in the central part, and Fig. 4 shows the shape of the whole pipe in a side view.
In an exemplary embodiment, the pipe of a fired heat exchanger is composed of three parts: the first cylindrical end 1A circular in cross-section followed by the corrugated flattened central part 2, which on the other side transitions into the second cylindrical end 1B. Both sections 3 of the transition between the cylindrical ends 1A, 1B and the corrugated flattened central part 2 are spherical in shape. The corrugated flattened central part 2 of the pipe has two essentially parallel walls 4, and each wall has two grooves which run along the whole length of the wall and form inward ribs 5, where the ribs on the opposite pipe walls 4 form opposite rib pairs, none of which contacts any other. In this way, the distance between the parallel walls 4 of the pipe in the area of the opposite ribs 5 in the flattened central part 2 of the pipe narrows down to a crevice. Along its length, the surface of the flattened central part 2 is waved, where the length L, i.e. the distance between two adjacent peaks, decreases from the first end 1A towards the second end 1B. Also the wave amplitude H and the distance D between the essentially parallel walls 4 gradually decrease.
In an exemplary embodiment of the invention the pipe is made of stainless steel, its total length is ∼1240 mm, and the length of the waved flattened central part is ∼1000 mm. The diameter S of the cylindrical ends 1A, 1B of the pipe is ∼42 mm, and the thickness of the walls is ∼1 mm. In the waved flattened central section 2 of the pipe the wave length L changes from ∼121 mm to 70.6 mm, the wave amplitude H changes from ∼26 mm to ∼19 mm, and the distance D between the essentially parallel walls 3 narrows down from ∼14 mm to ∼9 mm.
In other embodiment variants the structural details and individual dimensions may differ depending on the requirements and structure of the heat exchanger in which the pipes are installed. In specific embodiments the number of inward ribs 5 on parallel walls 4 of the flattened central part 2 may be different, or there may be no ribs at all. Also the number, length, and amplitude of waves along the flattened central part may be different. For specific needs the pipe may have only one spherical section, i.e. one end circular in cross-section which transitions into the flattened part, this solution, however, reduces the strength of the other end of the pipe.
In known pipes with changing cross-section designed for the flow of combustion gases in fired heat exchangers, the section of transition from the part circular in cross-section to the flattened part with two essentially parallel walls is formed into a flattened funnel, i.e. the walls of the transition section are flat. In the pipe according to the invention, however, the transition section 3 between those two parts different in cross-section is spherical in shape, which is obtained particularly through hydroforming. The spherical shape substantially increases the strength since the distribution of stress caused by the very high external pressures to which the pipe is exposed in the heat exchange chamber of the heat exchanger is even on circular-spherical surfaces. This particular shape of section 3 improves the strength of the pipe in this critical area and allows for reducing the thickness of the pipe walls and pipe diameters without deteriorating the working parameters. The spherical shape of the section of transition between the cylindrical ends and the flattened central part improves the strength of the pipe in those areas. The changing amplitudes and periods of the waves in the central part of the pipe cause turbulences of the fumes flowing through, and this in turn improves the transfer of heat to the pipe walls. When flowing through the pipe, hot fumes the volume of which at the inlet is large and flow speed high, cool down losing in volume, which in turn reduces the speed. The gradually shrinking cross-section of the pipe helps to equalise the speed of fumes, thus equalising the turbulences and allowing for even transfer of heat. The pipe of a fired heat exchanger, according to the invention demonstrates substantially improved heat exchange parameters as compared to the known solutions.

Claims

Pipe for a fired heat exchanger said pipe having a changing cross-section and at least one cylindrical end being circular in cross-section said at least one cylindrical end transitions into a corrugated flattened central part (2) with two essentially parallel wall, the pipe is characterised in that the section (3) of transition between the at least one cylindrical end (1A, 1B) and the corrugated flattened central part (2) is spherical in shape.
Pipe according to Claim 1, characterised in that the wave length (L) and amplitude (H), as well as the distance (D) between essentially parallel pipe walls (4) in the corrugated flattened central part (2) of the pipe change along the pipe length.
Pipe according to Claim 2, characterised in that the wave length (L) and amplitude (H) in the corrugated flattened central part (2) of the pipe and the distance (D) between the essentially parallel pipe walls (4) decrease smoothly along the pipe length.
Pipe according to Claim 3, characterised in that there are lengthwise grooves along opposite walls (4) of the corrugated flattened central part (2) of the pipe, which form inward ribs (5).
Pipe according to Claim 4, characterised in that there are two ribs (5) on each of the opposite walls (4) of the corrugated flattened central part (2), forming two opposite pairs of ribs (5).
Pipe according to Claims 1 - 5, characterised in that the diameter (S) of the cylindrical ends (1A, 1B) is less than 50 mm, and the thickness of the walls does not exceed 1 mm.