Soot blower

The soot-blower is embodied by a double tube which is disposed in a heat exchanger surface formed of straight welded-together tubes. The double tube soot-blower is formed of two concentric tubes with nozzles extending radially between and secured to the respective tubes. The inner tube is adapted to be supplied with a soot-blowing medium and the nozzles are arranged to blow the medium across the face of a heat exchanger surface or wall. The nozzles may be of one-piece construction or multi-piece construction.

This invention relates to a soot blower and, more particularly, to a soot 
blower for a heat exchanger. 
Heretofore, it has been known to construct heat exchangers with walls or 
heat exchanger surfaces made from welded-together tubes in order to define 
a chamber. In some cases, the surfaces have been formed with orifices 
through which soot blower lances having a soot blower nozzle at their tip 
can be introduced into the chamber so that steam or a high-pressure gas 
can be injected through the lance and nozzle to remove accumulations of 
soot and slag particles from the surfaces. This system has proved 
satisfactory in cases in which the pressure in the chamber where the 
deposits build up is substantially the ambient pressure. However, in other 
cases, complicated closure facilities must be provided for the orifices. 
Further, such facilities are expensive and may cause difficulties in 
operation. In addition, particular disadvantages arise for the case in 
which the heat exchanger surface is the wall of a pressure vessel or is 
surrounced by a pressure vessel wall. 
Accordingly, it is an object of the invention to provide a soot blower 
which is suitable for use in a flue passage at a positive pressure of more 
than 10 atmospheres absolute. 
It is another object of the invention to provide a soot blower for a heat 
exchanger which is of simple construction. 
It is another object of the invention to provide a soot blower for a heat 
exchanger which does not require closure devices. 
It is another object of the invention to provide a simple technique for 
blowing soot from the walls of a heat exchanger. 
Briefly, the invention provides a soot blower which is comprised of a 
double tube including an inner tube for conveying a soot-blowing medium 
and an outer tube which defines an annular gap with the inner tube as well 
as a plurality of nozzles. Each of these nozzles is connected to the inner 
and outer tubes for conducting the soot-blowing medium from the inner tube 
out of the outer tube. 
In one embodiment, each nozzle is made of one piece construction and is 
disposed radially of the tubes. 
In another embodiment, each nozzle includes a body which is sealingly 
secured to each of the tubes and a hollow insert which is adjustably 
mounted in the body. In addition, the insert is shaped to define a 
constriction in order to form a jet of the soot-blowing medium during use. 
The soot blower is particularly useful in a heat exchanger which has at 
least one heat exchange surface including a plurality of parallel tubes. 
In this case, the double tube of the soot-blower is incorporated in the 
heat exchanger surface with the annular gap between the inner and outer 
tubes disposed on an axis parallel to the remaining tubes of the heat 
exchange surface. 
If the heat exchanger is constructed with a plurality of heat exchange 
surfaces defining a regular prism shape, each surface is provided with a 
double tube near a respective corner of the prism shape in order to direct 
a stream of soot-flowing medium along an adjacent heat exchange surface. 
The effect of this arrangement is that streams of soot-blowing medium 
graze over the adjacent heat exchanger surfaces to produce very strong 
scouring or removal forces. 
The invention also provides a method of clearing soot from a heat exchanger 
having a plurality of tubes defining heat exchange surfaces. In this 
regard, the method is comprised of the step of alternately delivering an 
intensive flow of soot-blowing medium to the inner tubes of each double 
tube for a short period of time and a leakage flow of soot-blowing medium 
to the inner tubes for a longer period of time. This helps to keep the 
consumption of high pressure soot-blowing medium at a reasonable level 
while also insuring that secondary flows of dirty flue gas are not formed 
by the inner tubes.

Referring to FIG. 1, the soot blower is comprised of a double tube 3 which 
includes an inner tube 1 for conveying a soot-blowing medium and an outer 
tube 2 about the inner tube 1 in order to define an annular gap 
therebetween. In addition, a plurality of nozzles 5 are sealingly secured 
to and between the tubes 1, 2 in order to conduct a soot-blowing medium 
from the inner tube 1 out of the outer tube 2. 
The inner tube 1 is provided with a plurality of apertures which are 
radially disposed (only one such aperture is shown) and the nozzles 5 are 
welded radially into the respective apertures. As shown, each nozzle 5 is 
of one piece construction and is in the form of a short tubular member 
which is turned conically at each end. For example, the entry side of the 
nozzle 5 adjacent the inner tube 1 is formed with a large cone apex angle 
while the exit side of the nozzle 5 is formed with a small cone apex 
angle. In addition, the nozzles 5 are sealingly secured, as by welding, to 
the outer tube 2. 
In order to construct the double tube, the inner and outer tubes 1, 2 are 
placed one within the other with the inner tube 1 secured in the outer 
tube 2 so as to lie along a generatrix. Thereafter, the two tubes 1,2 are 
drilled radially. Next, the inner tube 1 is removed and the nozzles 5 
welded thereto dead radially. Thereafter, the inner tube 1 with the 
nozzles 5 thereon is fitted into the outer tube 2 so that the nozzles 5 
register with the apertures in the outer tube 2. The inner tube 1 is then 
raised to the required position by means of suitable tools which are 
introduced into the nozzles 5 radially of the tubes 1, 2 and which engage 
behind the nozzles 5. Thereafter, the nozzles 5 are welded to the outer 
tube 2. 
Referring to FIGS. 3 and 4, the double tube soot-blowers are incorporated 
into a heat exchanger comprised of a plurality of heat exchange surfaces 
or walls formed of a plurality of parallel tubes. Generally, the heat 
exchanger surfaces form the walls of cooled flue passages. Each heat 
exchange surface is formed by parallel tubes 10 which are welded together 
via ribs 11 which are disposed centrally between adjacent tubes 10. The 
double tubes 3 are disposed in the plane of the tubes 10 near an edge 
between two tube walls. As indicated in FIG. 3, the heat exchange surfaces 
define a regular prism shape so that the double tubes are disposed near a 
respective corner of a prism shape. The tubes 3 are so turned that the 
nozzle axes are aligned substantially parallel to the adjacent wall or, at 
a slight angle thereto. 
As shown in FIG. 4, the nozzles 5 of two oppositely disposed tubes 3 
associated with the same wall plane are offset from one another so that 
fan-shaped zones of blown soot-blowing medium merge with one another. 
Referring to FIG. 2, the wall tubes 10 and the outer tubes 2 of each soot 
blower are connected to a distributor 20 while the inner tubes 1 extend 
through the respective outer tubes 2 in a bend a short distance above the 
distributor 20. 
Each outer tube 2 is drawn in near the bottom end and is welded into an 
orifice in the distributor 20. The wall tubes 10 adjacent the outer tube 2 
are bent in knee-fashion and are welded at an angle of approximately 
45.degree. into orifices in the distributor 20. The next adjacent wall 
tubes 10 extend in alternating manner in either a straight line fashion or 
in knee-fashion into the distributor 20. 
Referring to FIG. 4, each inner tube 1 is connected via a valve 25 to a 
soot-blowing medium accumulator (not shown) which is charged by a 
compressor (not shown). This blowing medium can be, for example flue gas 
from the flue passage defined by the heat exchanger. Conveniently, flue 
gas to be used for this purpose has substantially all suspended particles 
therein removed before being used as a blowing medium. 
Generally, the walls of the heat exchanger are cleaned in a cyclical 
manner. In this case, the valves 25 of the individual inner tubes 1 are 
briefly opened in an alternating manner. 
Alternatively, the valves 25 can have a reduced leakage so that a small 
quantity of blowing medium continues to be supplied to the nozzles 5 even 
when the valves 25 are in a closed state. This leakage feature insures 
that, when the valves 25 are in the closed state, there is no build up in 
the zones between the nozzles of the tubes 1 of a secondary flow which 
might carry ash and particles of slag into the inner tubes 1. 
Referring to FIG. 5, each nozzle may also be made of multi-piece 
construction. For example, each nozzle includes a body 6 in the form of a 
tubular member which is sealingly secured, as by welding, to and between 
the inner and outer tubes 1, 2. This tubular member 6 is provided with an 
internal screw thread and receives a hollow insert 7 in an adjustably 
mounted manner. As indicated, the hollow insert 7 defines a constriction 
to form a jet of soot-blowing medium. 
The invention thus provides a soot-blower which can be incorporated into 
the walls of a heat exchanger. As such, there is no need to provide a 
means for moving soot-blowing lances into and out of the heat exchanger 
for cleaning purposes. 
Further, the invention provides a technique for operating the soot-blowers 
of a heat exchanger in a manner which does not require individual closure 
devices for the nozzles of the soot-blowers. 
A heat exchanger which has a soot-blower rigidly connected therein is 
particularly suitable for situations where there is a positive pressure on 
the gas side. In this event, complicated facilities for moving the 
soot-blower are unnecessary.