This invention is related to a cleaning device for combustion devices and particularly to one for large scale combustion devices for the reduction of soot and/or slag encrustations forming on internal heat exchange surfaces.
During the combustion process of fossil fuels such as coal, the internal heat exchange surfaces of boilers and other combustion devices become encrusted with slag and soot. In order to enhance the thermal and combustion efficiency of such devices, it is necessary to reduce the amount of encrustations on the heat exchanger surfaces. Numerous techniques for boiler cleaning are in use today. One approach is the use of so-called sootblowers which project a stream of cleaning medium such as air, steam, or water, or mixtures of these materials against the internal heat exchange surfaces which cause the accumulated encrustations to be removed through mechanical and thermal shock.
Various types of sootblower systems are used today. One type of sootblower is positioned permanently inside a boiler and is actuated periodically to eject a sootblowing medium. Other types are retractable and include the so-called long retracting sootblowers having a long lance tube which is periodically advanced into and retracted from the heat exchanger. The lance tube features one or more nozzles at its distal end from which the cleaning medium is ejected. The retraction feature of these sootblowers enables the lance tube to be removed from the intense heat within the combustion device between the cleaning cycles which would otherwise damage the lance tube. In most applications of long retracting sootblowers the lance tube is simultaneously rotated as it is axially extended into and out of the boiler so that the stream of sootblowing medium traces a helical or oscillating path during the cleaning cycle. Sootblowers are normally operated intermittently in accordance with a schedule which considers cleaning requirements, sootblower medium consumption, boiler thermal efficiency, and various other factors.
In cases where steam or a mixture which includes steam is used as the cleaning medium and the sootblower is actuated intermittently, there is a tendency for liquid condensate to collect in the cleaning medium supply circuit and lance tube between actuation cycles. At the beginning of the next actuation cycle when the cleaning medium supply valve is opened, the collected condensate is ejected from the cleaning nozzles in the form of liquid slugs. In some conditions, when such slugs of condensate strike the boiler wall surfaces and heat transfer tubes, erosion occurs due to an excessive level of thermal and mechanical shock. Such degradation of the heat exchange components of a boiler can cause failures and limit the operating life of the boiler which is a significant financial cost for the boiler operator. In view of the foregoing, a need exists for a sootblower system which accommodates condensate slugs without causing boiler component damage.
In addition to concerns regarding condensed steam forming between actuation cycles, or at the beginning of a cleaning cycle, there are applications in which it is desirable to use saturated or low quality steam as the cleaning medium. In such applications, the presence of condensate is expected as part of the cleaning medium flow supplied to the sootblower lance tube during a cleaning cycle. It is accordingly desirable to provide a sootblower lance assembly which permits the use of such cleaning medium while separating and safely ejecting entrained condensate.
Various sootblower configurations are known which seek to avoid the disadvantages associated with ejection of condensate when using steam as the cleaning medium. An example of such designs is provided with reference to applicant's previously issued U.S. Pat. No. 5,063,632. Although such devices generally operate satisfactorily, they have a number of significant disadvantages. For example, in some instances, such devices choke the flow of cleaning medium due to interference between the opposed cleaning medium nozzles. Sootblower nozzles are designed to provide efficient conversion of the static and dynamic pressure of the supplied sootblowing medium into a stream ejected from the cleaning nozzle(s) which has a high cleaning effect or peak impact pressure. Fluid flow interference caused by a disrupted cleaning medium flow at the nozzle entrance may lead to performance degradation. Further disadvantages of known sootblower nozzle blocks for condensate ejection include the requirement of complex internal welded components which can become dislodged or deteriorate during use.
One known technique for reducing condensate ejected from the cleaning nozzles is to use a port at the distal end of the lance tube provided to allow the ejection of condensate at the terminal end along the longitudinal axis of the sootblower nozzle block. This approach, described in the previously referenced US patent, creates a continuously open flow path initially for condensate ejection but thereafter permits cleaning medium to escape. Since cleaning medium ejected along the lance tube longitudinal axis is, in most applications, not useful for providing a cleaning effect, this discharge flow constitutes an efficiency degradation of the sootblower's operating performance. An ejection port at the nozzle block distal end produces a spray of condensate into the boiler internal volume. Although, as mentioned previously, ejection of condensate in this direction typically does not lead to undesirable consequences, it is preferable that a port for condensate ejection acts as an “inefficient” nozzle, in terms of generating a coherent high velocity stream of condensate at a given supply pressure. Ideally the condensate spray pattern ejected from a condensate port would be highly dispersed with low impact pressure characteristics.
In sootblowing applications, it is desirable to preserve the supplied sootblowing medium's dynamic and static pressure as it is converted to a stream of cleaning medium emitted from the lance tube nozzles which provides a high dynamic cleaning effect. Accordingly, it is desirable to provide a nozzle block which provides the previously noted desirable features while maintaining excellent performance in terms of cleaning effect.
This invention is related to a sootblower system incorporating a novel lance tube nozzle block having features for reducing the quantity of condensate ejected from cleaning nozzles forming on the inside of the nozzle block, lance tube, poppet valve, and related plumbing passageways or entrained in the cleaning medium supply in a manner which does not lead to boiler tube erosion. The sootblower cleaning nozzles which are aimed at the heat transfer surfaces to be cleaned, spray a steam or a steam/air mixture relatively free of condensate. Accordingly, this invention is capable of substantially minimizing the erosive effect caused by an initial output of a slug of condensate, or condensate present in a steady-state condition against heat transfer surfaces in a boiler. The nozzle block in accordance with this invention provides a condensate separation feature and further a means for ejecting the condensate from the nozzle block in a manner which, for intended applications, does not cause boiler tube erosion. Furthermore, the condensate separating effect provided by the nozzle block in accordance with this invention allows the use of saturated steam or a steam/water mixture for the purposes of cooling the lance tube, while avoiding the degree of heat exchanger erosion which would occur if all the condensed or entrained liquid water were sprayed against the heat exchanger surfaces from cleaning nozzles.
The nozzle block in accordance with an embodiment of this invention is preferably formed as an integral casting and forms two separated flow paths for the cleaning medium. The flow is separated at about the diametric mid-plane of the lance tube inside diameter by a divider wall to define two separated flow paths dedicated to separate nozzles. Each of the flow paths travels to the terminal end of a nozzle block where it undergoes a sharp “U-turn” bend (i.e. about 180°) and then extends rearward and terminates at a sootblower nozzle for spraying the cleaning medium radially from the nozzle block. The two separated flow paths are intertwined within the nozzle block interior. In one embodiment, the terminal end of the nozzle block features a pair of elongated slot passageways which serve to provide an ejection port for condensate. A slot is provided for each of the flow paths and has a particular orientation with respect to the cleaning medium flow to enhance the condensate separation effect. While the slot provides an effective condensate separation effect, it's cross-sectional flow area remains small, resulting in a low percentage of cleaning medium passing through the slots not available for cleaning purposes.
Various embodiments of this invention are described. In one embodiment, the previously mentioned flow path orientations are provided with the condensate ejection slots. In a further embodiment, the interior nozzle flow paths have the features for guiding condensate adhering to the internal surfaces of the nozzle block passageways toward and out of the condensate ejection slots. A still further embodiment provides condensate ejection for a single distal end nozzle for a nozzle block which does not divide the flow paths between a pair of nozzles, or with features only a single distal end nozzle.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.