The invention is directed to a waste heat boiler for cooling a solids laden hot gas.

Such a waste heat boiler is described in US-A-2006076272. This publication describes a typical coal gasification process as performed in an elongated gasification reactor vessel. The hot gas, as it is discharged by the gasification reactor, needs to be deflected by 180 degrees in order to flow downwards in the waste heat boiler. In the design of US-A-2006076272 the deflection of the hot gas is done via a bent duct section of about 45° with the horizon, followed by a gas reversal chamber in which the gas is deflected by 135°. The gas reversal chamber is present at the upper end of the waste heat boiler. A disadvantage of the gasification configuration of the prior art design is that in operation solids may accumulate on the cooling surfaces and the support structure of the cooling surfaces as present in the waste heat boiler. The present invention aims at providing an improved waste heat boiler. This is achieved by the following waste heat boiler.

Waste heat boiler being an elongated vessel comprising a co-axial positioned tubular channel for hot gas, said channel further being provided with an inlet for hot gas and an outlet for cooled gas, wherein a gas pathway is defined between said inlet and outlet of said tubular channel and wherein in the gas pathway one or more bundles of tubular cooling surfaces are present, said tubular cooling surfaces positioned coaxial with the channel, wherein the tubular channel is closed at one end, thereby forming a gas reversal chamber, and wherein the gas inlet is an opening in the wall of the tubular channel positioned between the gas reversal chamber and the gas pathway, wherein the inlet for hot gas is connected to an inlet conduit, which conduit is positioned under an angle α with said tubular channel and wherein at the hot gas inlet in the tubular channel a diverter plate is present.

Applicants have found that by having such a plate present the gas flows more uniformly through the waste heat boiler. Because the gas velocities are more uniform almost no stagnant flow exists and therefore the solids do not have an opportunity to accumulate on the cooling surfaces and the support structure of the cooling surfaces and therefore, better heat transfer occurs.

The invention shall be further illustrated by making use of Figures 1-2.

Figure 1 shows the top end of a waste heat boiler according to the invention.

Figure 2 shows cross-sectional view AA' of Figure 1. Figure 1 shows the top end (1) of a waste heat boiler (2) being an elongated vessel (3) . The vessel (3) comprises a co-axial positioned tubular channel (4) for hot gas. The channel (4) is provided with an inlet (5) for hot gas and an outlet for cooled gas at the lower end of the vessel (3) (not shown in this Figure) . A gas pathway (6) is defined between said inlet (5) and outlet of said tubular channel (4) . In the gas pathway (6) one or more bundles (7) of tubular cooling surfaces are present. The bundles (7) of tubular cooling surfaces are positioned co-axial with the channel. The tubular channel

(4) is closed at one end (8), thereby forming a gas reversal chamber (9) . The gas inlet (5) is an opening in the wall (10) of the tubular channel (4) positioned between the gas reversal chamber (9) and the gas pathway (6) . The inlet (5) for hot gas is connected to an inlet conduit (11), which conduit is positioned under an angle α with said tubular channel (4) . Angle α is preferably between 30 and 90°. At these preferred angles the hot gas as it flows, in use, through inlet conduit (11) will make a bend of more than 90° when it flows into the gas pathway (6) . An example of the waste heat boiler (2) as described above is described in the aforementioned US-A-2006076272. Figure 1 also shows an additional diverter plate (12) at the hot gas inlet (5) in the tubular channel (4) . Such a plate can advantageously be added to a waste heat boiler of US-A-2006076272 in order to improve the flow pattern by equalising the gas flow and thus increasing the heat transfer. With the phrase at the hot gas inlet

(5) is meant: at the same elevation when the vessel (3) is positioned vertically, as will be the case when used for its intended application. In this manner at least some of the gas entering the tubular channel (4) will impinge on said diverter plate (12) when in use. The diverter plate (12) is preferably positioned under an angle β of between 5 and 45° with the longitudinal axis of tubular channel (4) with the top of the diverter plate rotated in the direction away from the flow of the incoming hot gas, as shown in Figure 1. More preferably, the diverter plate (12) is positioned under an angle β of between 10 and 25°, and even more preferably, under an angle β of 15° with the longitudinal axis of tubular channel (4) . In a preferred embodiment angle β can be altered. The plate preferably has a dimension and position in the tubular channel such that at least two main gas entry pathways (13 and 14) are formed for the hot gas flowing towards the gas pathway (6) . Preferably four gas paths are formed. One main gas entry pathway (13) will run via the gas reversal chamber (9) and one main gas entry pathway will run via an opening (15) directly connecting the gas inlet (5) and the gas pathway (6) . The two other gas paths (20a and 20b) are on the left and right side of the plate as shown in Figure 2.

Preferably plate (12) is provided with cooling means. More preferably the cooling means are one or more conduits (16) having inlets (17) and outlets (18) for a cooling medium as shown in Figure 2. A suitable cooling medium is chilled water or boiling water. Plate (12) is suitably supported by support rods (21) . The support rods (21) are suitably fixed at the four edges of a, preferred rectangular, plate (12) . The plate (12) may suitably be provided with one or more mechanical cleaning means (19) or a blaster to remove any solids that may accumulate during operation. The surface of the plate (12) may suitably be provided with a layer of refractory or with cladding. The uniformity of gas flow in waste heat boiler (2) was measured and analyzed with and without diverter plate (12) . The velocity distribution of the gas was measured along a horizontal plane perpendicular to the bundles (7) of tubular cooling surfaces 0.5 meters above the bundles (7) of tubular cooling surfaces and along a horizontal plane perpendicular to the bundles (7) of tubular cooling surfaces 0.5 meters into the bundles (7) of tubular cooling surfaces. The gas velocity distribution is best characterized by the standard deviation of the velocity magnitude or root mean square (RMS) of the velocity deviation from the average. RMS is a standard statistical method to evaluate how much a variable varies around its average value and is well known to those of ordinary skill in the art.

The RMS value of the gas velocity distribution at 0.5 meters above the top of bundles (7) of tubular cooling surfaces without the use of diverter plate (12) was 37.4% and with the use of diverter plate (12) positioned under an angle β of 20°, the RMS value was 5.2% and with the use of diverter plate (12) positioned under an angle β of 15°, the RMS value was 5.6%, both representing approximately a seven-fold improvement in gas velocity distribution versus the case where diverter plate (12) was not used.

The RMS value of the gas velocity distribution at 0.5 meters below the top of bundles (7) of tubular cooling surfaces without the use of diverter plate (12) was 8.5% and with the use of diverter plate (12) positioned under an angle β of 20°, the RMS value was 4.0%, and with the use of diverter plate (12) positioned under an angle β of 15°, the RMS value was 3.7%, both representing over a two-fold improvement in gas velocity distribution versus the case where diverter plate (12) was not used.

Thus, the use of the diverter plate (12) substantially increased the uniformity of gas velocity both above and within the bundles (7) of tubular cooling surfaces .