ES2591279B1 - Improved cooling system for steam generation boilers - Google Patents

Abstract

Cooling system for steam generation boilers for industrial applications formed by a shell and tube condenser in which the tubes are constructed using additive manufacturing technologies, so that said tubes have an internal wall that presents a plurality of separate obstacles each other both along the axial axis, and on the radial surface.

Description

Improved cooling system for steam generation boilers

OBJECT OF THE INVENTION

The present invention relates to a new cooling system concept for steam generation boilers for industrial applications, incorporating tubes with improved design that favor heat transmission and delay the appearance of biological encrustations.

BACKGROUND OF THE INVENTION

The boilers for steam generation are widely used systems at industrial level for diverse applications, being the most common in heating stages in the manufacturing process or the conversion to electricity through the turbination of the generated steam. However, the use of steam in industry also includes other applications such as sterilization, use as a motive fluid to move liquid or gas flows in pipes, for mechanical separation of fluids by atomization, for cleaning, as well as for hydration and humidification stages. in diverse processes, as per

15 examples of sintering materials.

All steam generation equipment, as in the case of boilers, integrates a cooling system or thermodynamic condenser, which by means of air or water condenses the remaining steam after carrying out its function and returning it to the boiler, or if necessary eliminating it through the corresponding water network. The air is used as a fluid

20 refrigerant only in cases where there is no water available for this function, since in this case the condensers have a low efficiency. In the case that the coolant is water, it is usually obtained from rivers (fresh water) or from the sea (salt water).

Cooling systems or water condensers are usually changers

25 tubular heat of the shell and tube type. In these devices, the water or cooling fluid circulates through the tubes and the remaining steam or cooled fluid circulates through the housing. The housing is usually made of carbon steel and the tubes, which are the elements that seek to exchange heat between water and steam, are usually made of stainless steel, when river water is used as a cooling fluid, and titanium when

30 uses seawater, due to the corrosion resistance needed in each case. In its lower part, the housing has a tank called a hot well that collects and accumulates the water that results from the condensation of the steam, from which the condensate extraction pumps suck.

The waters, both sweet and salty, are chemically solutions

35 complexes of inorganic and organic components, presenting different concentrations of ions, diverse chemical elements and dissolved gases that range from nitrogen, oxygen and carbon dioxide to others such as hydrogen sulfide, which is an important source of energy for some photosynthetic bacteria. From a biological point of view, there is a wide variety of organisms capable of adhering to a structure to produce an inlay, such as bacteria, cyanobacteria, algae, fungi and protozoa,

The phenomenon of fixing communities of encrusting organisms to a surface in contact with water is known as biological embedding or biofouling. These incrustations are especially harmful in the event that the phenomenon occurs inside the condenser tubes since the biofilm that appears embedded inside the tube, first produces a reduction in transmission efficiency. of heat, when the heat transfer coefficient is reduced and consequently the specific exchange surface is reduced, also altering the flow. Secondly, because the biofilm, in continuous growth, eventually clogs the tube, making it necessary to stop the boiler to completely clean the cooling system.

Logically, to avoid the growth of the biofilm, the levels of detachment of biofilm cells must exceed those of adhesion and reproduction thereof. Several studies have shown that shear stresses of the fluid on the embedded biofilm pennite the separation detachment or fractionation of portions of the reservoir.

Nowadays the means used to delay the growth of the biofilm are the mechanics and chemicals, such as the use of biocides. Documents such as GB2151744 (A), US4366003 (A), JPS62109999 (A) and CN101949545 (A) describe various mechanical systems to prevent fouling in heat exchanger tubes. On the other hand, W02012044409 (A1), W02011090830 (A1), W02009020694 (A1) and W02009154784 (A1), are documents that describe some existing systems to chemically remove biological encrustations from structures in general and tubes specifically.

It is also known that with the introduction of roughness in the walls of the tubes, the creation of secondary flows in the tube is favored, there are experiments and several numerical studies that have shown that they are responsible for an increase in heat transfer. In addition, because turbulent flows have very good mixing, it is usually convenient to operate the heat exchangers in turbulent regime, often by inserting turbulence-promoting obstacles. W02015007645 (A1), W02001086881 (A1), JP4550451 (B2) and CN 1 02353296 (A) describe improved interior designs and geometries in heat exchanger tubes to promote heat transfer.

Similarly, the literature shows us that in addition to the roughness of the inner surface of the tube, the coefficient of heat transmission in turbulent regime is also improved by creating eddies in the flow. In this regard, the displacement of the turbulence boundary layer is a mechanism of special relevance to increase heat transfer. Rabas and Arman (1992) characterized the phenomenon, concluding that a flow when an obstacle is found in a wall, creates a small area of recirculation both in the front part of the obstacle, as in the other side of the obstacle, regrouping the flow later until find a new obstacle and with the appearance of eddies along the area between obstacles. The authors observed increases in heat transfer both in the areas before and after the obstacle. On the other hand, Webb, Eckert and Goldstein (1971) studied the influence of the ratio between the height of obstacles (e) and distance between them (p), leading to ratios (p) / (e) between O, 75 ~ 1 , 25, a single recirculation eddy is generated that comprises the entire distance between obstacles, with two small eddies confined in the areas near the walls of the obstacles. Therefore, by introducing obstacles in the inner wall of the tubes separated by short distances from each other, it is possible to improve the efficiency of the heat exchange phenomenon, while creating eddies in the areas close to the wall that by recirculation of the fluid generate shear forces that prevent the creation of the precursor biofilm of biological encrustations.

The present invention intends to solve the limitations in the matter of heat transmission and resistance to the appearance of biological fouling of the current cooling systems for steam generation boilers. For this, a new concept of cooling pipes is described, improved by means of a design of structures inside the tube that allow, on the one hand, to increase the specific surface of heat exchange, favor the creation of secondary flows and cause turbulent flow through roughnesses in the wall internal tube, as well as generate eddies that cause backflows.

The interior design of these improved tubes does not allow their manufacture through conventional processes such as extrusion, and must be constructed using additive manufacturing technologies.

Additive manufacturing or 3D printing, terms that are already used interchangeably today, refers to a set of manufacturing processes that consist of adding material, usually layer by layer, building a real piece from a 3D data file, such as a CA030 file.

The different manufacturing processes with this type of technology basically consist of the manipulation of the material on a micrometric scale, depositing it very precisely to build a solid. In this way, the desired geometry is generated by adding material from a virtual geometry, without the use of preforms or molds and without subtracting material. In general terms it is a process of progressive addition of material to the piece and the consolidation of said material in its position. The construction material can be provided in various forms such as solid powder, solid rod or wire, constant thickness sheet or liquid.

These types of technologies are used today to build, for example, physical models, prototypes, mold components, tools as well as final pieces in various plastic, metal, ceramic and vitreous materials. The applications of these parts and components are also varied, for example in consumer goods, industry, health or military.

The current state of the art of additive manufacturing technologies allows the manufacture of components in various materials, plastics, ceramics and metals. In the case of metals, today there are several additive technologies, the most common being powder bed systems (power-bed systems), with laser-based solutions and electron beam (electron beam), as well such as powder-fed systems, also known as laser recharge (Iaser cladding) and laser metal deposition (Iaser metal deposition).

Additive manufacturing provides the advantage of proportional design freedom in components, precisely because of its manufacturing characteristic by adding material. In this way it is possible to construct the geometries of the cooling system object of the present invention, allowing the construction of metal tubes in materials such as stainless steel and titanium with the required internal structures to favor the turbulence and backflows necessary to favor heat exchange and delay the appearance of the biofilm that causes biological fouling.

DESCRIPTION OF THE INVENTION

The invention relates to a new concept of cooling system for steam generation boilers for industrial applications that incorporates tubes with an improved design that favors heat transmission and delays the appearance of biological scale.

A first aspect of the invention relates to a cooling system for steam generation boilers for industrial applications consisting of a shell and tube condenser. Through the tubes, built using additive manufacturing technologies, the coolant circulates, which can be fresh water or seawater. Through the confined space between the tubes and the housing envelope, steam and condensates from the boiler circulate and deliver their heat to the coolant, decreasing its temperature. Each tube of the condenser has in its internal wall various protrusions, distributed along the axial axis of the tube and its radial surface and which turn out to be obstacles to the advance of the cooling fluid through the tube.

The application of additive manufacturing technologies makes it possible to construct the tubes object of the invention, in metallic materials such as stainless steel (suitable for fresh water) or titanium (suitable for sea water), which otherwise would not be technically feasible. Thus, it is possible to construct the geometries of tubes with internal obstacles in their interior walls. The obstacles have a ratio between their height (e) and distance between them (p) with values between 0.75-1.25, ensuring the generation of a single recirculation swirl that includes the entire distance between obstacles, with two small swirls confined in areas near the walls of obstacles. In this way it is possible to improve the heat transmission for the cooling of the steam and condensates that circulate through the housing, while creating backflows that generate shear stresses along the tube wall and prevent the creation of the precursor biofilm of Biological inlays

According to another aspect of the invention, the cooling system tubes described above have roughness on their inner face, generating secondary flows of the cooling liquid in the tube, in addition to increasing the active heat exchange surface, with the consequent increase in transfer of heat

The construction of the tubes by means of additive manufacturing technologies allows to provide the desired roughness in case to the inner walls of the tube, and can be modified depending on the area of the tube and depending on the heat exchange coefficient required in each zone of the condenser.

According to another aspect of the invention, the obstacles present in the inner walls of the tubes are equidistant from each other along their axial axis and on the radial surface thereof.

According to another aspect of the invention, said obstacles have the same regular geometry, such as hemispheres, prisms or cubes.

According to another aspect of the invention, the obstacles can be continuous along the radial surface of the tube, being separated from each other by a certain distance along the axial axis.

According to another aspect of the invention said continuous obstacles along the radial surface of the tube are equidistant from each other along the axial axis.

According to another aspect of the invention, said continuous obstacles along the radial surface of the tube have the same regular geometry, such as, for example, semi-cylindrical.

or prismatic

According to another aspect of the invention, the tubes constructed by additive manufacturing are manufactured using laser selective metal sintering technology.

DESCRIPTION OF THE FIGURES

A series of drawings that help to better understand the invention and that expressly relate to embodiments of said invention, which are presented as illustrative and non-limiting example thereof, will now be described.

Figure 1. Scheme of the integral parts of the complete cooling system, consisting of a shell and tube condenser.

Figure 2. Diagram of a cross-section of the tube along its axial axis and representation of the eddies and backflows that originate between obstacles for values of the obstacle height ratio (e) and distance between them (p) between 0, 75-1, 25.

Figure 3. Diagram of a sectional section of the tube shown in Figure 2 as well as representation of the corresponding eddies and backflows.

Figure 4. Diagram of a cross-section of the tube along its axial axis, the inner surface of the tube presenting a certain roughness.

Claims (8)

one.

Cooling system for steam generation boilers for industrial applications consisting of a condenser (1) with at least one housing (2) and at least one tube (3) constructed using additive manufacturing technologies, characterized in that the at least one tube ( 3) it has an internal wall (4) that presents a plurality of obstacles (5), which consist of an extension of the wall towards the inside of the tube and that are separated from each other along the axial axis (6) of the less a tube (3) as well as on the radial surface of the at least one tube (3).

2.

The cooling system for steam generation boilers for industrial applications according to claim 1, characterized in that the inner wall (4) has a rough surface (7).

3.

The system according to any of the preceding claims, characterized in that the plurality of obstacles (5) are equidistant from each other along the axial axis (6) and on the radial surface of the at least one tube (3) in which they are arranged.

Four.

The system according to any of the preceding claims, characterized in that the plurality of obstacles (5) have the same regular geometry.

5.

The system according to any one of claims 1 to 2, characterized in that the plurality of obstacles (5) consist of a continuous extension of the wall into the tube along the radial surface of the at least one tube (3), being separated from each other by a certain distance along the axial axis (6).

6.

The system according to the preceding claim, characterized in that the plurality of obstacles (5) are equidistant from each other along the axial axis (6).

7.

The system according to any of claims 5 and 6, characterized in that the plurality of obstacles (5) have the same regular geometry.

8.

The system according to any of the preceding claims, characterized in that the at least one tube (3) has been constructed by the technology of additive manufacturing of selective sintering of metal by laser.