This application relates to improvements in the construction and operation of a water tube boiler comprising a housing containing upper and lower left and right water manifolds. Tubes connect the left manifolds and other tubes the right manifolds. The tubes are bent toward one another to form a plurality of superposed chambers through which combustion gases must successively flow, from front to back in one chamber and from back to front within the next.
In U.S. Patent 4,355,602 there is described a simple boiler of the abovementioned type which is relatively simple and inexpensive to manufacture and operate. That boiler comprises a housing having a top provided with a gas outlet, bottom, left and right sides and a front and back, the housing containing an upper manifold and a lower manifold substantially parallel to the top, bottom and side walls, two sets of tubes, each set comprising a plurality of tubes, one set joining the upper manifold to the lower manifold on the left and the other set joining the upper manifold to the lower manifold on the right, the tubes of each set rising from the lower manifold upwardly along their respective side wall, crossing the housing to the opposite side wall, rising adjacent the opposite side wall re-crossing the housing to their respective side wall, rising therealong and eventually joining the upper manifold, the horizontal runs of the tubes of one set being vertically offset relative to the horizontal runs of the tubes of the other set so as to form a plurality of superposed chambers, individual tubes of the sets being differently bent so as to form access openings from each chamber to the chambers above and below, the openings from chamber to chamber being front to back and the next chamber from back to front, means for introducing liquid into one of the manifolds and for withdrawing the liquid from the other manifold, and means for introducing a hot gas into the lower-most of the superposed chambers, the hot gas rising successively through the chambers which it successively and alternatively traverses from front to back and then from back to front until it exits from the uppermost chamber through the gas outlet in the top, liquid flowing through the manifolds and tubes being heated by the hot gas, at least one baffle within at least one of the chambers extending from top to bottom and from one of the sides toward but terminating short of the other, whereby hot gas traversing that chamber from front to back is additionally forced to flow laterally to get around said baffle.
It is an object of the present invention to improve the efficiency of operation of such a boiler by simple structural modifications and by simple procedural demands.
These and other objects and advantages are realized in accordance with the present invention by means of a boiler having the features of the first part of Claim 1, in which at least one upper and at least one lower manifold project from the inside of the housing to the outside, a downcomer outside the housing connects the top of the lower manifold and the lowest part of the upper manifold, thereby permitting the boiler to operate within a shallow level of water in the upper manifold, speeding up circulation of water and its heating, and permitting substantially dry steam to be discharged from the upper manifold, and a baffle (or baffles) is angled within its chamber so that the hot gas hits it at an angle less than 90° so as to be deflected thereby in the direction of its advance, thereby avoiding hot spots, and further successive chambers of the boiler are reduced in volume from bottom to top to make up for the reduction in volume as the hot gas cools, thereby keeping the gas velocity high and maintaining turbulence which helps heat exchange.
The invention will be further described with reference to the accompanying drawings, wherein:
Referring now more particularly to the drawings, in Figure 1 there is shown a housing 10 having a top wall 12, a bottom wall 14, a left side wall 16, a right side wall 18, a front wall 20 and a rear wall 22. A lower manifold 24 and an upper manifold 26 project through the front and rear walls 20 and 22. Means are provided to introduce cold water into the lower manifold at 28 and to remove steam from the upper manifold at 30, outside the housing.
A downcomer 32 outside the housing connects the lowest part of the upper manifold 26 with the top of the lower manifold 24 so that water in the upper manifold can rapidly run down for reheating, speeding up the circulation. This also permits the upper manifold to operate with a shallow level of water which also speeds up production of steam and which permits substantially dry steam to be discharged from the upper manifold 26.
A plurality of tubes 36, illustratively twenty- three, extend from the left upper manifold 26 to the left lower manifold 24 and a similar number of tubes 38 extend from the right upper manifold 26 to the right lower manifold 24. Except for the first 36a and last 36c few tubes in each set, for a reason to be described later, the balance of the tubes 38b are all similarly bent as are the tubes 38.
Each tube has a vertical component and tubes 38a and 38b have two horizontal components, i.e. one run to the left side of the boiler, or actually to the tubes 36, and then a return run. The bends in tubes 38 are not identical to those of tubes 36 but rather complementary so that together they form a series of vertically superposed chambers 40a, 40b, 40c, 40d and 40e, decreasing in volume from bottom to top to make up for reduction in volume as the hot gas cools, thereby keeping the gas velocity high and maintaining turbulence which helps heat exchange.
Advantageously, the boiler has five, seven or nine chambers. Combustion gases in chamber 40a rise through such space and enter chamber 40b traversing it horizontally from back to front. The tube bends similarly cause the gases to traverse successive chambers until they reach the topmost chamber 40e where they exit through an opening in the top 12.
For improved heat exchange, in addition to the tortuous gas flow so far defined, a more complex flow is possible. Thus rectangular baffles 46 having the shape shown in Figure 5 may be provided, extending from adjacent one side wall toward but short of the other. They are just high enough to span a chamber being held in position by their fit between the troughs formed by adja- centtubes. They are inserted by simple sliding and may be removed, or slid more or less into their chambers, either manually or automatically (not shown), as desired.
If more than one baffle 46 is present in a given chamber they must alternately extend from opposite sides. Thus, while the combustion gas is moving from rear to front in chamber 40b the gas stream must move from side to side to get around the baffles.
As shown in Figures 4 and 5 the baffles have front and rear elements which are high and low enough to lodge in the nips between adjacent tubes. In between there is a lower section which is just high enough to clear the minimum vertical space of the chamber. This section is arranged at an angle less than 90°C, e.g. about 45° so the gas will be deflected off it in a direction which will help advance the gas, thereby avoiding hot spots.
In Figures 1 and 3 it can be seen that the connections between the tubes and upper manifold are not in a straight line but rather are staggered. However, all the tubes join the upper manifold at or belowthe upper manifold's horizontal center line and each tube in going from lower to upper manifold has lengths which rise or are horizontal but has no lengths which go downwardly, thereby avoiding entrapment of gas.
The baffles can serve a further purpose, viz. maintaining efficient utilization of fuel notwithstanding fluctuating fuel feed rates as a consequence of fluctuation in steam demand. Specifically, one monitors the oxygen content of the hot gas exiting the boiler which otherwise will change as feed and demand vary. However, the position of the baffle or baffles is adjusted to maintain this oxygen content substantially constant, e.g. as demand goes down the oxygen content will go up, so the baffle positions will be adjusted to give more baffling and thereby restore the oxygen level to the predetermined value.