US3478725A - Water tube boiler - Google Patents

Description

No v. 18, 1969 J MUNSTER ETAL 3,478,725

WATER TUBE BOILER Filed Sept. 14, 1967 .4 Sheets-Sheet l 62 26 AL 0 F/gJ 2B 5 3 76 22 H J.Y T 7 J. MUNSTER ET AL WATER TUBE BOILER Nov. 18, 1969 Filed Sept. 14, 196'? .4 Sheets-Sheet 2 In ventosr Nov. 18, 1969 J. MUNSTER ETAL- 3,478,725

WATER TUBE BOILER 4 Sheets-Sheet 5 Filed Sept. 14, 1967 In ventors:

Nov. 18, 1969 U NSTER ETAL WATER TUBE BOILER .4 Sheets-Sheet 4 Filed Sept. 14, 1967 Fig.4

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United States Patent 3,478,725 WATER TUBE BOILER Josef Munster, Dusseldorf-Oberkassel, Gerd Wellensiek,

Hosel, and Gunter Linke, Dusseldorf-Urdenbach, Germany, assignors to Ferdinand Lentjes Dampfkesseluntl Maschinenbau, Dusseldorf-Oberkassel, Germany, a corporation of Germany Filed Sept. 14, 1967, Ser. No. 667,766 Claims priority, application Germany, Sept. 20, 1966,

Int. Cl. uzzb 21 /30 U.S. Cl. 122333 8 Claims ABSTRACT OF THE DISCLOSURE A water tube boiler having a contact heating chamber above a radiation chamber. The water is circulated down through an outer basket of downcomer pipes and up through an inner basket of riser pipes both surrounding the radiation chamber. At the transition between the two chambers the riser pipes are gathered together and merge continuously into a bundle of tubes extending up the centre of the contact heating chamber so that the rising gases are confined within a smaller cross-section as they flow up through the bundle.

Heating a boiler with a gas under pressure has been known ever since the development of the Velox boiler. Recently this method of heating has acquired importance in connection with the partial oxidation of liquid or gaseous fuels, which undergo a chemical transformation during the partial oxidation and are then cooled by the water circulating in a boiler. The gases being cooled in this way are under a high pressure which can be anything between and approximately 120 atmospheres gauge, depending on the nature of the gas and of the process used. However a boiler of the kind mentioned at the beginning can, as an alternative be heated by hot flue gases obtained by normal combustion of liquid or gaseous fuels.

The already known heat exchangers or waste heat recovery boilers are constructed essentially on the principle of the fire tube boiler. But the increasing gas pressures and temperature and the high power requirements are making it increasingly difiicult to utilise the gases effectively for producing steam. The thermal stresses produced in fire tube heat exchangers by the high gas temperatures and pressures are reaching values beyond what the available materials of construction are capable of withstanding. Heat exchangers of this kind are therefore limited to comparatively low throughputs of the order of 30,000 Nm. /hour and gas pressures of up to 50 atmosphere gauge.

The high gas pressures and temperatures result in particular in very high heat transfer rates near the inlet ends of the heat'transfer surfaces. These high heat transfer rates largely determine the wall temperatures of the structural elements in this region. The inlet gas distributor in a fire tube boiler must therefore be so designed that the thermal stresses due to the high wall temperatures, and in particular clue to the great temperature difference between the gas side and the water side of the wall, remain within tolerable limits. A consequence of these circumstances is that for a particular material of construction there is a corresponding upper limit to the permissible wall thickness, and this in turn determines the size of the distributor, particularly its diameter, and this limits the power throughput of the heat exchanger. A further difficulty arises from the fact that a fire tube boiler is sensitive to attack by corrosion, due to the high 3,478,725 Patented Nov. 18, 19 69 "ice wall temperatures, particularly by hydrogen sulphide, a substance which is often produced by partial oxidation of a fuel in the presence of a high concentration of hydrogen. This kind of corrosion can be prevented by using expensive chromium steels, but this remedy has two disadvantages. In the first place it increases the cost of the installation and secondly the chromium steels have low heat conductivities and this again increases the wall temperatures and makes stress problems more difficult.

The object of the present invention is to provide a boiler heated by gases under pressure and capable of handling much higher gas throughputs than have hitherto been possible. In particular the intention is to keep the temperatures of the materials of construction as low as possible both on the gas side and on the water side of the wall, without using any insulating material, so as to keep the thermal stress problems within the limits already prevailing in water tube boiler construction. One of the particular advantages obtained in this way is that the heat transfer materials nowhere reach temperatures so high that it becomes necessary to use expensive chromium steels to counter corrosive attack.

In contrast to the heat exchangers which have hitherto been developed for the chemical purposes mentioned at the beginning, the present invention is a development from water tube boilers, that is to say boilers through whose tubes there circulates water or a steam-water'mixture, the heating gases flowing over the outsides of the tubes. The present invention therefore relates to a water tube boiler with convective or forced circulation of the working medium, and with a radiation chamber through which hot gases pass upwards to a contact heating chamher. The gases will usually enter the radiation chamber under high pressure and at temperatures above 1200 C.

In accordance with the invention, in such a boiler, the radiation chamber is surrounded by an outer basket of downcomer tubes and an inner basket of riser tubes which protect the outer basket from radiant heat, the upper parts of the riser tubes being gathered together towards the axis of the boiler, and merging without any interposed collector into a closely crowded tube bundle which extends up through the contact heating chamber and provides surfaces over and through which the gases and the working fluid both flow in the same direction, the tubes in the bundle being so close together that the cross-sectional area of the passage available to the flowing gases in the contact heating chamber is less than onefifth of the cross-sectional area available to the gases in the radiation chamber.

Although the riser tubes forming the second basket are grouped closely together, this is not intended to imply that there is a gastight seal between these tubes. On the contrary the tubes should be grouped only so close together that theyprotect the downcomer tubes of the outer basket, and also the outer pressure vessel itself, from the heat of the gases under pressure, which is almost exclusively given off by radiation, while at the same time leaving sufficient gaps between them to allow pressure equalisation between the inner space of the radiation chamber and the annular spaces between the tube baskets and between the outer tube basket and the wall of the pressure vessel. It should be observed that there are no heat insulating materials, in the form of layers of substances having low heat conductivities. Insulation against heat is provided exclusively by the tube baskets.

In a boiler constructed in this way the inner basket of riser tubes absorbs the radiant heat in the lower and hotter part of the boiler, where the gases give off heat mainly by radiation, and in this way protects the outer basket of downcomer tubes, and also protects the pressure vessel, of the radiant heat. The radiation chamber, through which the gases pass before reaching the convection part of the boiler, cools the heating gases down to 1200 C. or less, before they enter the convection part. This reduces the heat load near the inlet of the convection passage, and reduces the temperature of the heat transfer material here, at the same time eliminating the risk of H 8 corrosion in the presence of high concentrations of hydrogen. In the boiler according to the invention deposition of soot, coke and other solid impurities on the convection chamber surfaces is prevented in that the crosssectional area of the passage available to the flowing gases decreases in the transition region between the radiation chamber and the convection chamber to a small fraction of its previous value, less than one-fifth and even as low as one-fortieth. This constriction in the gas passage increases the linear speed of the gas by a factor between and 40. It has been found by experience that this increased velocity has a self-cleaning effect which largely prevents deposition of solids.

The diameter of the radiation chamber is determined by the required mass rate of flow in the convection part, and by the number of tubes which are therefore required. This gives the diameter of the radiation chamber, assuming that the tubes are closely grouped together. The length of the radiation chamber is determined by the required final temperature. In designing the convection part of the boiler, the tube diameter can be increased, compared to what it is in the radiation chamber, so as to shorten the tubes, and thus shorten the enire boiler, for a given heat transfer area.

Preferably the gas passage in the contact heating chamber is subdivided longitudinally, that is to say in the direction of the tubes, into at least two separate passages leading to two separate effluent gas outlets which can be individually shut off. With this arrangement the flow to either of the two gas passages can be entirely interrupted, with the result that the velocity of gas flow in the other passage, or passages, is considerably increased, producing a much greater self-cleaning efiect.

In order to provide a wall around the outside of the tube bundle forming the contact heating chamber it would be posible to install an external jacket around the tubes. However, the wall may be formed simply by welding together the outermost tubes of the bundle.

In the contact heating chamber the tubes are crowded very closely together, leaving for the passage of the gas hardly more than the sum of the geometrical gaps between each three tubes. A narrow passage of this kind favours heat exchange between the hot gas and the steamwater mixture, but makes it comparatively difiicult for the gases to escape finally from the tube bundle in radial directions. In order to facilitate the necessary final escape of the gases, a gas collector chamber is mounted over the contact heating chamber. Extensions of the riser tubes penetrate through this gas collector chamber and here the external diameter of each tube is reduced, com-' pared to what it is in the convection chamber. In this way larger gaps are obtained between the individual tubes, allowing the gases to escape sideways quite easily into the gas collector chamber.

The construction of the boiler according to the invention is so elfective in preventing deposition of soot, coke and other impurities on the water tube external surfaces that a mechanical cleaning is necessary only after long operational periods, if at all. However, in order to allow mechanical cleaning to be performed, the upper ends of the riser tubes may issue into an effluent gas collector chamber which is removably attached to the boiler, in such a way that after loosening the attachments which hold the collector chamber to the boiler the entire tube system can be lifted clear out of the boiler.

The already known heat exchangers which take heat from partially burnt gases are usually connected to their combination chambers by lengths of pipe. It is a particular advantage of the boiler according to the invention that no connecting pipes are used here. The boiler can be directly attached to the combustion chamber, in which the heating gas is produced by partial or normal combustion.

One example of a boiler constructed in accordance with the invention is illustrated in the accompanying drawings, in which:

FIGURE 1 is a longitudinal section through the boiler;

FIGURE 2 is a section taken on the line II-II in FIGURE 1;

FIGURE 2a is an enlarged fragmentary view of the tube system as shown in FIG. 2;

FIGURES 2b and 2c are longitudinal views respectively of the most left-hand and most right-hand riser tubes of FIG. 2114 showing several rods for mutually connecting adjacent riser tubes;

FIGURE 3 is a section taken on the line IIIIII in FIGURE 1; and

FIGURE 4 is a section taken on the line IVIV in FIGURE 1.

In the drawing there have been omitted the burner working in the combustion chamber, the arrangements for supplying the feed water, and the pipes for taking away the steam. Moreover in FIGURE 1 all the water tubes are represented as single full lines, that is to say not as double lines. Refractory ceramic material is shown in section cross hatched.

The boiler shown in FIGURE 1 consists of a pressure vessel 6 in the form of an essentially cylindrical steel jacket, the lower end of which is closed by a hemispherical dome 8 having a flange rem-ovably connectible by bolts 74 to a corresponding flange 72 on the steel jacket. The upper end is closed by a cover 10 attached by screws to the flange of the pressure vessel. To give an idea of the size of the boiler the diameter of the pressure vessel can, merely by way of example, be approximately 1 to 3 m., and the overall length approximately 30 m.

The pressure vessel 6 contains a series of four chambers one above the other. The lower chamber is a combustion chamber 12, which has a bottom opening 13 into which is inserted the burner, which is not shown in the drawing. The combustion chamber is lined with refractory material 14. When the boiler is operated in the ordinary way, that is to say using the usual combustion process, the burner supplies to the combustion chamber compressed air or oxygen together with a gaseous fuel or a fog of liquid fuel. On the other hand, when the boiler is used as a cooler for a gas decomposed by partial combustion, then there is fed to the combustion chamber 12 through the burner (not shown) a fog of oil, in steam and oxygen, or alternatively natural gas and oxygen without any steam.

Above the combustion chamber 12 the pressure vessel 6 contains a radiation chamber 16 into which the normal or partly burnt heating gas flows through a channel 18. The radiation chamber 16 is surrounded by two tube baskets, which will be described in greater detail further below. In the radiation chamber the heating gas gives its heat to the surroundings mainly by radiation.

Above the radiation chamber 16 the pressure vessel 6 contains a convection or contact heating chamber 20, which consists of a tube bundle, which will also be described in greater detail further below. The tube 'bundle takes up heat from the heating gas mainly by convection. The fourth chamber of the boiler is a collector chamber 22 and from here the heating gas, which has by now become comparatively cool, leaves the boiler through the pipe connections 24.

The part of the boiler which constitutes the essential core of the invention is the water tube system. This is connected, in the manner customary in water tube boilers, to a drum 26 containing a water space 28 and a steam space 30. The water space 28 is connected by a few tubes 32 to an annular distributor 34 situated just under a wall 36 made of a refractory material. The wall 36 is a gastight bulkhead separating the gas collector chamber 22 from an annular chamber 54 surrounding the convection chamber 20. The annular chamber 54 will be mentioned again further below. When the boiler is operated with forced water circulation, a pump is interposed between the drum 26 and the annular distributor 34. Starting from the annular distributor 34 a number of downcomer water tubes 38 extend downwards to near the bottom of the combustion chamber 12. The downcomer tubes lie clme together close to the inner surface 40 of the pressure vessel 6, forming the outer tube basket already mentioned above. At their lower ends the downcomer tubes 38 curve around through 180 at 42 to become the riser tubes 44, there being as many riser tubes as there are downcomer tubes. From here the riser tubes extend upwards parallel to each other and close together. Where the riser tubes 44 reach the upper end of the radiation chamber 16 they all curve over inwards, or are angled inwards, to form a central tube bundle 46, the tubes here being closely spaced together as shown in cross-section in FIGURE 3. A point of great importance in the present invention is that there is no collector whatever interposed between the riser tubes in the radiation chamber and those in the convection bundle 46, the riser tubes all extending smoothly and without interruption from their lower ends all the way up to where they issue at the top of the boiler. The inclined parts of the riser tubes, where they gather together in the region 48 in FIGURE 1, are covered over by a layer 50 of refractory material, so that the gases after issuing from the channel 18 and passing through the radiation chamber 16 are then compelled to pass along a comparatively constricted passage consisting of the space remaining between the tubes of the tube bundle 46. To retain the gases within this constricted passage the tube bundle 46 is sealed off all the way around its periphery. This is done in quite a simple way by welding iron rods 52 between the outer tubes, one rod between each two tubes, as shown in FIGURE 3. The ion rods extend all the way up the tube bundle. The gases therefore flow upwards inside the tube bundle 46, and no gases flow through the surrounding annular chamber 54. However, due to unavoidable leakage of gases, an effect which in this case is not undesired, the pressure in the annular chamber 54 is the same as the heating gas pressure inside the tube bundle 46. The temperature in the annular chamber 54 is that of the steam-water mixture in the tubes. The steam pressure is usually chosen to' be higher than the pressure of the heating gas, so that heating gas can never leak through into the steam-water spaces.

At this point it should be mentioned that the riser tubes 44 in the radiation chamber 16 are also connected together by interposed rods 56 as shown in FIGS. 2a, 2b and 2c, but only in order to give the tube basket greater mechanical strength. These rods, that is to say the rods 56 in FIGS. 2b and 2c, consist of short lengths of rod attached at intervals.

In order to reduce the length of the pressure vessel the tubes in the convection part of the boiler have larger diameters than those in the radiation part, as already mentioned above and as represented in FIGURE 1. Above the refractory bulkhead 36 the riser tubes 44 continue in the form of tubes 58 whose external diameters are reduced, compared to the riser tubes in the convection chamber 20, as represented in FIGURE 4. This is to give more room for radial escape of the heating gases through the gaps between the tubes. Finally, the tubes 58 issue to a collector 60 which is connected by tubes 62 to the steam space 30 of the drum 26, completing the water-steam circuit.

When the boiler is in operation the heating gas flowing from the combustion chamber 12 into the radiation chamber 16 gives up its heat mainly by radiation to the riser tubes 44 which form the inner tube basket. The riser tubes absorb this heat and prevent any significant amount from reaching the outer tube basket consisting of the downcomer tubes 38, the amount finally reaching the jacket of the pressure vessel 6 being very little. During the passage of the gases through the radiation chamber 16 their temperature falls from the initial value of about 1800 C. at the inlet down to about 1200 C. The heating gases under pressure tend to deposit soot, coke and other impurities. This difliculty is overcome in the boiler according to the invention in that at the transition from the radiation chamber 16 to the convection chamber 20 the cross-sectional area of the passage available to the heating gases decreases at least to one-fifth of its previous value and under certain circumstances, depending on the type of gas handled and on other conditions, decreases to one-fortieth of its previous value. The gases flow through the spaces between the riser tubes in the convection chamber at a greatly increased velocity, and the resulting sustaining efiect ensures that the passages remain almost entirely free from deposits. From here the gases pass into the collector chamber 22 and then issue from the boiler through the pipe connections 24.

For the reasons mentioned at the beginning it is advisable to subdivide the cross-section available to the gases in the convection chamber into separate channels. For this purpose the present version of the boiler has a longitudinal wall which subdivides the convection channel into two halves. This longitudinal wall is constructed quite simply by welding together a number of tubes near the longitudinal medial plane of the tube bundle, as shown at 64 in FIGURE 3, so as to form a gastight partition separating the passage for the heating gas into two separate channels, one for each of the gas outlet connections 24. The partition is continued in the collecting chamber 22 in the form of a full separation bulkhead 66. Outside the boiler, as represented in FIGURE 1, and out beyond the pipe connections 24, there are gas valves 76 allowing one or other of the two gas outlet pipes to be shut off or throttled. When the gases are prevented in this way from escaping through one of the gas outlet connections, the velocity of gas flow through the other half of the convection chamber is almost doubled, .with the result that the self-cleaning effect is greatly increased. In the version represented in the drawing the convection passage is subdivided into two halves, but by using more separating walls and more gas outlet connections the passage for the gasesdcan be further subdivided and different elfects produce The riser tubes 44 extend upwards to connect with a cover 68 which is screwed to the upper part of the boiler. Loosening the screws indicated by centre lines in the drawing, and loosening further connections, allows the cover 10, together with the entire tube system which remains attached to the cover 10, to be lifted upwards right out of the pressure vessel 6, for cleaning and repair purposes. However in view of the method of functioning of the boiler, as described above, this becomes necessary only after a quite unusually long period in service.

We claim:

1. A water tube boiler of the kind comprising means for producing circulation of the WOI'kirlg medium, a radiat on chamber, a contact heating chamber above said radiation chamber, and means adapted to provide hot gases for upward passage through said radiation chamber and contact heating chamber, chracterised in that said radiation chamber is surrounded by an outer basket of downcomer tubes, and an inner basket of riser tubes in fluid flow communication with said downcomer tubes, at least an outer layer of said riser tubes incorporating means for forming a substantially gas-tight seal thereabout so as to protect said outer basket from radiant heat, and in that a closely crowded tube bundle extends up through said contact heating chamber and provides heat exchange surfaces for said gases and working fluid flowing in the same direction, said riser tubes having portions thereof gathered together and merging towards the axis of said contact chamber, said tube bundle extending directly from said portions substantially at and along said axis and being so compact as to provide in said contact heating chamber a cross sectional area of passage available to said flowing gases less than one-fifth of the cross sectional area available to said gases within said radiation chamber.

2. A boiler according to claim 1, characterised by at least one separating wall adapted to subdivide said gas passage through said contact heating chamber into at least two separate passages, separate gas outlets communicating one with with each of said separate passages, and means adapted individually to shut-off said separate gas outlets.

3. A boiler according to claim 1, characterised by means welding together outer tubes of said tube bundle to provide a surrounding wall for said contact heating chamber to retain said gases in said contact heating chamber.

4. A boiler according to claim 1, characterised by a gas collector chamber above said contact heating chamber, extension of said riser tubes passing therethrough, said extensions having external diameters less than those of said riser tubes in said contact heating chamber.

5. A boiler according to claim 1, characterised by an increase in the diameters of said riser tubes in the region of transition from said radiation chamber to said contact heating chamber.

6. A boiler according to claim 1, further characterised by an enclosing pressure vessel, a gas tight cover, and means supporting said tubes from said cover whereby said tubes can be lifted with said cover as a unitary assembly out of said pressure vessel.

7. A boiler according to claim 1, further characterised by a gas inlet for said radiation chamber, a combustion chamber adapted to produce heating gases by partial oxidation or by normal combustion under pressure, and means directly connecting said combustion chamber to said gas inlet.

8. A boiier according to claim 7, further characterised by means removably connecting said combustion chamber to said pressure vessel.

References Cited UNITED STATES PATENTS 2,547,135 4/1951 Mercier 122333 2,603,559 7/1952 Patterson 122-333 X 2,672,849 3/1954 Fruit 122333 2,672,850 3/1954 Loughin et a1 122--333 FOREIGN PATENTS 806,997 1/1959 Great Britain.

CHARLES J. MYHRE, Primary Examiner

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