WO2021186100A1

WO2021186100A1 - Hybrid nozzle

Info

Publication number: WO2021186100A1
Application number: PCT/FI2021/050151
Authority: WO
Inventors: Kalevi KURKI; Ilkka Mänttäri
Original assignee: Im Serco Oy
Priority date: 2020-03-19
Filing date: 2021-03-02
Publication date: 2021-09-23
Also published as: FI129821B; FI20205283A1; EP4121695A1

Abstract

The invention relates to an air nozzle of a recovery boiler for feeding air required for the combustion process into the furnace of the boiler. The air nozzle according to the invention comprises a body (1) removably attached to the tube wall of the boiler furnace, on the outside of the tube wall, and an insert (2) removably attachable to the body (1) of the air nozzle from the inside of the furnace, which when connected together form a continuous tubular channel for feeding air into the boiler furnace.

Description

Hybrid nozzle

This invention relates to an air nozzle of a recovery boiler according to the preamble of claim 1. The primary uses of the air nozzles of the invention are in boiler plants related to the chemical wood processing industry, more particularly to the manufac turing process of cellulose, developed for the recovery of chemicals and production of energy, which are referred to in the technical language as recovery boilers. The invention may also be applied in other kinds of boiler plants in which the conditions in the furnace cause durability issues for the air nozzles, for example as a result of the erosion and corrosion brought on the by intense chemical wear or the flow of flue gases.

The invention is characterized by that which has been defined in more detail in the characterizing part of the independent claim. Structural solutions related to the im plementation of the invention and additional details supplementary to the independ ent claim have been defined in the dependent claims.

Air nozzles are used to lead preheated combustion air into the boiler furnace in or der to control the combustion process to make it so that it is as complete as possi ble. The air nozzles are positioned on the walls of the boiler furnace at different heights and typically, on opposing walls at each height level. The air nozzles are in stalled in through holes formed in the tube walls of the boiler furnace. Air to be fed through the air nozzles is led to the air nozzles in a pressurized state from distribu tion channels arranged outside the boiler furnace, connecting to each air nozzle. Based on the geometry of the air nozzle flow port and by adjusting the air volume on a nozzle-specific basis, the aim is to achieve a desired air supply distribution or coverage at different height levels as required to achieve an optimal combustion process. Finnish patent publication FI120550 discloses by way of example a solution for positioning air nozzles on the furnace walls.

The combustible matter of a recovery boiler, black liquor, is fed to the furnace as droplets of a desired size through nozzles designed for supplying combustible mat ter. Resulting from the supply of combustible matter in droplet form and the controlled feed of combustion air, a controlled combustion process is achieved in the furnace.

The air nozzles of a recovery boiler are critical components for the function of the boiler, and their operating conditions are highly demanding. The temperature of the furnace at different air nozzle height levels ranges typically between 600 and 1200 degrees Celsius. In addition to the issue of corrosion brought on by the high tem perature, the combustion gases are highly corrosive caustic gases.

For the air nozzles, a particular problem arises from the turbulent flow forming at the discharge end of the air nozzle, which when combined with the solid particles in the combustion gases causes intense erosion and corrosion at the tip of the air noz zle as well as crevice corrosion at the joint of the tip of the air nozzle discharge end and the opening tubes of the air nozzle installation opening. As a result of the high temperature and the turbulent flow, the thin tip parts of air nozzles currently in use tend to burn, causing damages to the tip and a need for regular maintenance. The turbulent flow causes intense erosion particularly on the opening tubes delimiting the through hole of the boiler furnace tube system. Damage to the tips of the air nozzles currently in use is due to a large part to insufficient cooling of the nozzles and the low structural thickness at the tip of the nozzle.

Air nozzles currently in use are typically welded plate structures or, to an increasing extent, cast components. Nozzles currently in use have a type of structure where they are only partially in contact with the opening tubes of the installation opening, resulting in limited cooling of the air nozzles. The air nozzles currently in use are typically installed and replaced from the outside of the furnace wall tube system, further making their replacement cumbersome, as the air supply channels and regu lating devices and accessories located outside the furnace will have to be disassem bled at least at the nozzle location to allow replacing the air nozzles.

The need for maintenance and regular replacement brought on by the technical is sues related to the above-described air nozzles cause significant servicing costs, particularly in the form of boiler outages, during which the entire cellulose manufacturing process is typically forced to a stop due to the maintenance of the recovery boiler.

Next, some typical air nozzle structures are described with reference to examples of publications found in patent literature.

Finnish patent publication FI 103904 describes a cooling solution for a plate nozzle, wherein air blown into the furnace is utilized in cooling the air nozzles.

Finnish patent publication FI 104993 discloses a structural solution for an air nozzle, in which the flow channel of a plate air nozzle is fitted with a massive add-on part, the material-technical properties of which, according to the publication, improve the durability of the nozzle with respect to both an improvement in the cooling and re sistance to smelt splattering. The solution is developed particularly for so-called pri mary air nozzles located near the smelt area at the bottom of the boiler.

Japanese publication JPH10298887 describes improving the corrosion resistance of an air nozzle by material-technical means by using a special doping.

Finnish patent publication FI 100429 discloses an air nozzle construction with a plate-like structure, wherein the nozzle housing of the air nozzle is gas-tightly mounted as a fixed structure in the tube wall of the furnace and a separate replace able nozzle head part with a plate-like structure is positioned within the nozzle housing. A welded joint is mentioned as one embodiment of the gas-tight attach ment of the nozzle housing to the furnace wall. The publication does not propose a solution for cooling the air nozzles nor for eliminating the issue relating to the turbu lent flow causing wear to the nozzle tip and the adjacent opening tubes. The solu tion is developed particularly for so-called primary air nozzles located near the smelt area at the bottom of the boiler.

The structure of the air nozzle according to the invention presented herein allows eliminating the above-described technical issues and thereby significantly decreas ing the direct and indirect costs associated to maintenance. The invention is characterized in that the air nozzle comprises two separate struc tural parts able to be partially nested inside one another, namely a body and an in sert, which when connected together and installed in connection with the boiler constitute a tubular air nozzle. The body of the air nozzle is removably attached to a structure located in the tube wall outside the boiler furnace, for example an installa tion housing. The insert to be removably connected to the body of the air nozzle is installed in connection to the body of the air nozzle from the inside of the furnace. The collar of the discharge end of the insert is shaped such that it seals the seam between the insert and the opening tubes of the air nozzle installation opening as tightly as possible. Where necessary, the sealing may be supplemented with a thin seal between the surfaces. The body of the air nozzle is a durable component, the maintenance or replacement need of which has been able to be eliminated with the solution according to the invention. The body of the air nozzle is installed outside the tube wall of the furnace. The need for disassembling the air distribution chan nels and regulating devices during replacement of the insert is also completely elimi nated, thereby minimizing the effort required for the maintenance of the air nozzles. The detachable connection between the insert and the body is secured with a me chanical connection member.

The invention is further characterized in that the cooling of the insert is rendered more effective by shaping the insert in such a manner that the contact surface with the boiler tubes is maximized in order to improve the convection-based cooling. The solution enables reducing the heat load particularly at the discharge end of the in sert.

The invention is further characterized in that the collar of the discharge end of the insert protects the opening tubes of the installation opening of the air nozzle, whereby the phenomenon of the turbulent flow at the interface of the insert and the opening tubes can be eliminated to a large extent.

Next, the invention is described with reference to the drawings, in which: Figure 1 shows the placement of the collar (10) of the insert (2) of the air noz zle installed in place in the installation opening as viewed from the in side of the furnace,

Figure 2 shows the section A to A of figure 1, and

Figure 3 shows the section B to B of figure 1.

Figure 1 shows the placement of the collar (10) of the insert (2) of the air nozzle in stalled in place in the installation opening as viewed from the inside of the furnace. The opening tubes (4) delimiting the installation opening in the tube wall structure of the furnace are shaped such that the installation opening is formed between bent tubes (4). A typical furnace tube wall structure consists of vertical boiler tubes (4), between which there is a plate-like fin (5) as a welded structure. In the figure, the collar (10) of the insert (2) partially covers the opening tubes (4) delimiting the in stallation opening, at most to the level of the center line (6), whereby the effect of the turbulent flow caused by the air flow from the nozzle on the opening tubes (4) delimiting the installation opening can be minimized. The edge of the insert collar is indicated with the reference number (7) in the figure.

Figure 2 shows the section A to A of figure 1. The body (1) of the air nozzle is re movably attached to an installation housing (3), which is an integral part of the boiler tube system. The insert (2) of the air nozzle is installed in place in such a manner that it abuts against a connection surface in the body (1). When installed in place, the body (1) and the insert (2) of the air nozzle form a flow channel for an air flow (8). The insert (2) is removably attached to the body (1) such that in addition to the connection surface in the body, it abuts against the surface of the opening tubes (4) and the fin (5) between the opening tubes (4). The fastening of the insert (2) to the body (1) is secured with locking means known per se from the inside of the air opening of the air nozzle, for example with a locking pin.

Figure 3 shows the section B to B of figure 1. The body (1) and insert (2) of the air nozzle are shaped such that their convectional surfaces are as large as possible on the surfaces facing the opening tubes (4). This shaping enables maximizing the cooling effect on the air nozzle components brought on by the water flowing in the opening tubes (4). Cooling of the insert (2) is a critical factor for the service life of the air nozzle. In the figure, the conventional surface of the body (1) and the insert (2) against the opening tube (4) is depicted with a dot-and-dash line.

The principal solution of the invention and some preferred structural embodiments have been presented above. However, the invention is not limited to the embodi ments presented herein, but the basic principle of the invention can be applied to various embodiments while keeping within the scope of the inventive idea defined in the independent claim.

Claims

1. An air nozzle of a recovery boiler for feeding air required for the combustion pro cess into the furnace of the boiler, characterized in that the air nozzle comprises a body (1) removably attached to the tube wall of the boiler furnace from the out side of the tube wall, and an insert (2) removably attachable to the body (1) of the air nozzle from the inside of the furnace, which when connected together form a continuous tubular channel for feeding air into the boiler furnace, and that one end of the insert (2) has a collar (10) abutting against the opening tubes (4) delimiting the air nozzle installation opening when the insert (2) is installed in place, which col lar is dimensioned such that it covers the opening tubes (4) delimiting the air nozzle installation opening in the tube wall of the furnace at most to the level of the center line (6) of the opening tubes (4) and is shaped on its surface on the side facing the boiler tube system so as to correspond to the shape of the surface of the opening tubes (4) delimiting the installation opening.

2. The air nozzle according to claim 1, characterized in that the first end of the insert (2) is shaped so as to correspond to a connection surface in the body (1) and that the first end of the insert (2) is inside the body (1) when the insert (2) is con nected to the body (1).

3. The air nozzle according to claim 1, characterized in that the body (1) is re movably attached to an installation housing (3) fixedly installed on the exterior sur face of the tube wall outside the boiler furnace.

4. The air nozzle according to claim 1, characterized in that the body (1) abuts at least partially against the opening tubes (4) delimiting the installation opening and is shaped at its end on the boiler tube side so as to essentially correspond to the surface shape of the opening tubes (4) in order to enhance cooling of the body.

5. The air nozzle according to claim 1, characterized in that the connection be tween the insert (2) and the body (1) is secured by means of a mechanical fas tening means, such as a screw fastening or a locking pin.

6. The air nozzle according to any of claims 1 to 5, characterized in that the body (1) and the insert (2) are manufactured from a metal material resistant to high tem peratures, mechanical wear and intense chemical corrosion by means of casting.