GB2209586A

GB2209586A - Tunnel-type waste-heat boiler

Info

Publication number: GB2209586A
Application number: GB8720970A
Authority: GB
Inventors: Zalman Leivikovich Berlin; Vladimir Nikolae Zakrividoroga; Gennady Vasilievich Maslovsky; Anatoly Gavrilovich Serkov; Boris Nikolaevich Chefranov; Viktor Yakovlevich Yakimovich
Original assignee: PROIZV OB BELGORODSKY Z ENERGE
Current assignee: PROIZV OB BELGORODSKY Z ENERGE
Priority date: 1987-09-07
Filing date: 1987-09-07
Publication date: 1989-05-17
Also published as: GB8720970D0; AU7794887A; AU595925B2

Abstract

The waste-heat boiler comprises a water-walled furnace chamber 1 and an adjoining horizontal convective gas duct 2 with tubular heating surfaces constituted by vertical platens 8, 9. The platens 8, 9 adjoin a crown 10 of the gas duct 2, are made in at least two given sizes as to height alternately lengthwise of the duct, and are evenly distributed across the width of the gas duct 2. By arranging the platens more thickly in the crown of the gas duct, the gas is partly directed downwardly to flow around the lower portions of the platens. The boiler has particular application to waste gases from non-ferrous metallurgical furnaces and the wood-pulp and paper industry. <IMAGE>

Description

TUNNEL-TYPE WASTE-HEAT BOILER The invention relates to apparatus for recovery of secondary power resources, and more particularly to a tunnel-type waste-heat boiler.

The invention can find most efficient application in non-ferrous metallurgy, in situations where it is fairly difficult to recover heat of dust-laden waste furnace gases with a relatively low softening temperature which might result in progressive scale deposits on the waste-heat boiler heating surfaces. The invention can also find utility in other industries, say, in the wood-pulp and paper industry, where gases to be recovered contain low-melting carried-away matter.

Our times witness the ever-growing application of tunnel-type waste-heat boilers with a main gas duct arranged horizontally as a tunnel, which accommodates tubular heating surfaces in the form of platens located one by one in the path of the gas flow.

The advantage of tunnel-type wast-heat boilers is that they provide optimum conditions for preventing progressive scale deposits on the heat-transfer tubes.

This is achieved by many factors, and first and foremost by the fact that the heat-transfer tubes are arranged mostly vertically, whereas in other embodiments the tubes feature horizontal or inclined arrangement.

Scale deposition is known to be largely determined by the flow rate of the dust-laden gas. Should it be low, the scale deposits on the tubes are generally non-coherent and may, therefore, either come down spontaneously or be easily removed by any known method.

A waste-heat boiler is known whose heating surfaces evenly fill in the gas duct throughout width and height (SU-A-254521). However, with the gas flow velocity in the boiler being fairly low, the gas flow segregates into a number of layers, most of which occur in the gas duct crown and, therefore, decrease efficiency of the lower portions of heating surfaces.

A tunnel-type waste-heat boiler is also known (SU-A-629431) whose horizontal gas duct is separated by means of a baffle into a radiant chamber and a convective gas duct accommodating throughout heating surfaces which are in fact vertical platens. The baffle is provided in the upper portion of the gas duct and the gas flow reaching the baffle reverses its direction, entering the lower portion of the convective gas duct, which ensures a uniform distribution of gas among the heating surfaces.

Yet, with the direction of the gas flow reversed so sharply, the carried-away dust is separated to give rise to large lumps of sintered dust deposited on the baffle. Thei-r weight can reach several tons in the course of one or two weeks of boiler operation. The dust lumps per-iodically fall in, thus damaging the platen tubes in the lower portion of the boiler.

Another drawback of such baffles is that they comprise horizontal tubes and hence can not be integrated with the steam-generating circuit of a natural-circulation boiler. In this way, a circulating pump and appropriate valves and accessories are required.

What is desired is a tunnel-type waste-heat boiler in which platens are arranged in the gas duct so as to ensure intensive heat transfer in the boiler, the gas temperature and velocity characteristics being adjusted throughout the gas duct cross section.

The present invention provides a tunnel-type waste-heat boiler comprising a water-walled radiant furnace chamber and an adjoining horizontal convective gas duct with heating surfaces which are substantially vertical platens, in which the platens adjoin the gas duct crown and are made in at least two standard sizes as for height, the platens being evenly distributed across the width of the gas duct.

In the tunnel-type waste-heat boiler disclosed herein, the platens are more thickly arranged in the crown of the gas duct than in its lower portion whereby gas temperature and velocity characteristics in its cross section are adjusted. This is achieved due to the fact that gas partly flows downwards around the lower portions of the platens despite the fact that the gas duct has no cross baffles.

The reversed gas flow being directed downwards, i.e.

along the gravitational forces, leads to separation of carried-away dust and allows its deposition in dust bins provided in the lower portion of the gas duct. As a result, it is unlikely that any deposition will occur on the platen tubes, especially in the gas duct crown, which makes heat transfer fairly intensive since it is there that most of the heating surfaces are located.

Thus, variations in thermal and velocity characteristics of the gas flow in the cross section of the horizontal duct in the tunnel-type waste-heat boiler are offset by platens so arranged in the gas duct that the gas flow temperature and velocity are adjusted throughout its height. This enables one to select optimum parameters of heat-dispersing and heat-absorbing media which determine design features of the heating surfaces and the boiler in general.

In the preferred embodiment of the invention, the short platens are in fact radiating water walls.

With the boiler in operation, the radiating water walls are heated until their temperature equals that of the gas flow, after which they transfer heat onto the adjacent surfaces. As a result, heat transfer from the gas flow to the heat-absorbing surfaces becomes intensive. In addition, the radiating water walls can be closely spaced in the gas duct crown inasmuch as they require no cooling medium.

It is expedient that platens of different height alternate throughout gas duct length. This eliminates formation of a number of parallel flows in the gas duct featuring different thermal or aerodynamic characteristics.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic longitudinal section view of a tunnel-type waste-heat boiler; Figure 2 is a section on line II-II in Figure 1; and Figure 3 is a section on line III-III in Figure 2.

The tunnel-type waste-heat boiler illustrated comprises a water-walled radiant furnace chamber 1 and an adjoining horizontal convective gas duct 2. The radiant chamber 1 has an inlet port 3, whereas the convective gas duct 2 has exhaust ports 4. Banks 5,6,7 of heating surfaces (evaporator platens, super-heated, air heater) are located in the gas duct 2 lengthwise.

Each of the banks 5,6,7 comprises vertical platens 8,9 (Figure 2) of at least two standard sizes evenly distributed throughout the width of the gas duct, viz.

long and short platens, respectively, whose upper portion adjoins a crown 10 of the gas duct 2. Some of the short platens platens 9 are in fact radiating water walls made, say, of metal, ceramics, or a combination thereof.

The platens 8,9 are evenly distributed in the gas duct 2 lengthwise (Figure 3).

The lower portion of the gas duct 2 accommodates bins 11 for collection and subsequent removal of carried-away dust.

The tunnel-type waste-heat boiler operates as follows.

Hot off-gases, say, in non-ferrous metallurgy enter the radiant chamber 1 through the inlet port 3 as shown by the arrow A and, upon cooling partially therein, flow into the horizontal convective gas duct 2 around the banks 5,6,7 of the heating surfaces in succession, and finally flow outside through the exhaust ports 4 as shown by the arrow B. There is practically no hot gas flow in the crown 10 of the gas duct 2 due to natural convection, resulting from the fact that the platens 8 and 9 are closely spaced therein. Gas partly flows downwards into the lower portion of the gas duct 2 filled in only with lower portions of the platens 8. In this case, gas temperature and aerodynamic characteristics are adjusted throughout the gas duct 2 both in its width and length. Carried-away dust is deposited in the bin 11. With no sharp reversal of the gas flow direction, there occur no heating surface deposits, which contributes to intensive heat transfer in the boiler. All this ensures high and stable technical and economic ratings of the waste-heat boiler as regards cooling of dust-laden flue gases and partial deposition of carried-away dust.

Claims

Claims:

1. A tunnel-type waste-heat boiler comprising a water-walled radiant furnace chamber and an adjoining horizontal convective gas duct accommodating surfaces constituted by substantially vertical platens adjoining a crown of the gas duct, the platens being of at least two given sizes as to height and being evenly distributed across the width of the gas duct.

2. A waste-heat boiler as claimed in claim 1, in which shorter ones of the platens constitute radiating water walls.

3. A waste-heat boiler as claimed in claim 1 or 2, in which platens of different height alternate in the gas duct lengthwise.

4. A tunnel-type waste-heat boiler substantially as described with reference to, and as shown in, the accompanying drawings.