Field of the invention

The invention relates to a steam generating system comprising

- a steam generator having a water jacket and at least one heating tube extending therein for the passage of a heat transfer medium,

- a steam drum arranged above the steam generator,

- at least one riser pipe for connecting the water jacket of the steam generator hydrauli- cally to the steam drum to enable the steam to be passed into the steam drum,

- at least one downpipe for connecting the steam drum hydraulically to the water jacket of the steam generator to enable the water to be returned from the steam drum to the water jacket of the steam generator.

The invention furthermore relates to use of this steam generating system.

Prior art

Steam generating systems of the type described at the outset are known from the prior art, e.g. from International Application WO 2011/104328 A2. In many cases, especially if a hot gas is to be used as a heat transfer medium, the steam generator is designed as a horizontally arranged, cylindrical shell-and-tube heat exchanger. A shell-and-tube heat exchanger of this kind and the use thereof to cool hot synthesis gas is described by European Patent EP 2312252 B1 , for example.

Here, the hot gas is passed through the heating tubes of the tube bundle, while the wa- ter to be evaporated is in the jacket space. A pre-heater, which is often likewise designed as a shell-and-tube heat exchanger, can be arranged downstream of the steam generator, as regards the heat transfer medium, and a superheater can be arranged upstream. A "steam drum", often likewise a horizontally arranged pressure vessel, is installed above the steam generator. The steam drum and the steam generator are con- nected to one another by riser pipes and downpipes. This enables the water/steam mixture to be circulated, thereby enabling the steam to be discharged efficiently from the steam generator and making possible more effective heat transfer at the surface of the heating tubes of the steam generator. If the steam drum can be positioned at a sufficient distance above the steam generator, this circulation can operate as natural circulation. If there is not sufficient space available for this, pumps must assist circulation. The term "forced circulation" is then used.

To prevent steam entering the downpipes, these are attached as low as possible to the circumference of the steam generator, often between the 4 and the 8 o'clock position if the cross section of the steam generator is imagined as a clock face. To achieve these positions on the underside of the steam generator jacket, therefore, the downpipe coming from above must be routed in an arc, the lowest point of which is still below the lowest point of the steam generator jacket. As a result, a minimum distance of the steam generator from the ground is required, resulting in design and setup-related restrictions during the planning of such systems, e.g. reactor supports have to be arranged at a minimum height.

The laterally attached supports for the downpipes furthermore induce forces on the jacket of the steam generator, namely static forces due to the deadweight of the down- pipes and due to thermal expansion forces, as well as dynamic forces due to wind and earthquake loads. As a result, considerably greater wall thicknesses of the supports and of the pressure jacket may be required, especially in the case of a special form of the design of such systems in which the weight of the steam drum is borne by the down- pipes and riser pipes. It was therefore the object of the invention to propose a steam generating system in which the disadvantages described are avoided.

Description of the invention

The object is achieved by a steam generating system in accordance with the features of Claim 1.

Steam generating system according to the invention:

Steam generating system comprising

a) a steam generator having a water jacket and at least one heating tube extending therein for the passage of a heat transfer medium,

b) a steam drum,

c) at least one riser pipe for connecting the water jacket of the steam generator hy- draulically to the steam drum to enable the steam to be passed into the steam drum, d) at least one downpipe for connecting the steam drum hydraulically to the water jacket of the steam generator to enable the water to be returned from the steam drum to the water jacket of the steam generator,

characterized in that

e) the downpipe, coming from the steam drum, passes in its upper half through the water jacket of the steam generator and extends therein as far as its lower half.

The steam generating system according to the invention makes it possible to position the steam generator close to the ground since the down pi pes no longer form the lowest point of the system. This simplifies the design of the upstream and downstream system components. The elimination of the downpipe inlet supports situated between the 4 and the 8 o'clock position means that forces are no longer introduced laterally into the jacket of the steam generator. The jacket can therefore be produced with a smaller wall thickness. The low points of the downpipes laid according to the previous prior art each had to be provided with a drain fitting. These fittings are eliminated in the system according to the invention.

Compared with the corresponding prior-art system, the space requirement for setting up the steam generating system according to the invention is reduced since there are no longer any laterally projecting downpipes, these being routed downward within the apparatus.

Preferred embodiments of the invention

A preferred embodiment of the invention is characterized in that the steam generator and the steam drum are arranged in such a way relative to one another, and the riser pipe and downpipe are designed in such a way that the water to be evaporated can be moved between the water jacket of the steam generator and the steam drum by natural circulation. This eliminates the installation of pumps and the associated outlay on main- tenance and repair as well as investment costs.

An alternative embodiment of the invention is characterized in that at least one pump is installed to assist water circulation between the water jacket of the steam generator and the steam drum. Even if there is no space for an adequate distance between the steam drum and the steam generator, sufficient water circulation can be achieved in the steam generator in this case.

Another preferred embodiment of the invention is characterized in that the steam generator and the steam drum are designed as horizontally arranged, cylindrical pressure vessels. The cylindrical shape with correspondingly arched ends has long proven its worth in the construction of apparatus and can be produced at low cost. The horizontal arrangement allows a lower overall height and hence good accessibility of the system.

Another preferred embodiment of the invention is characterized in that the riser pipes and the downpipes enter the water jacket of the steam generator in the 0 o'clock position and enter the steam drum jacket in the 6 o'clock position. In this way, the pipes can also be used as structural elements for supporting the steam drum.

Another preferred embodiment of the invention is characterized in that the steam gen- erator is designed as a shell-and-tube evaporator. This type of construction has long proven its worth in the construction of apparatus and can be produced at low cost.

Another preferred embodiment of the invention is characterized in that the downpipe is passed around the heating tube or heating tubes within the water jacket of the steam generator, as far as the steam generator volume region situated thereunder. As a result, there is virtually no effect on the construction of the heating tubes by the downpipes, and expensive design measures are not required in this region.

Another preferred embodiment of the invention is characterized in that the downpipe is passed through the heating tube bundle within the boiler. As a result, the downpipe or downpipes can run in a straight line, thereby keeping the flow resistance in the pipe low.

The invention furthermore also relates to the use of a steam generating system according to the invention, consisting in that the steam generating system is arranged down- stream of a steam reforming reactor and the synthesis gas emerging from the steam reforming reactor is used as a heat transfer medium in the steam generator of the steam generating system. The steam reforming of hydrocarbons to give synthesis gas, in many cases carried out with catalytic assistance in a tubular reactor, takes place with a high expenditure of energy and at high temperatures. The synthesis gas produced in this process leaves the reactor at a temperature of over 800°C. In order to utilize the thermal energy contained therein, the synthesis gas is used as a heat transfer medium to operate a steam generating system according to the invention.

Illustrative embodiments

Further features, advantages and possible uses of the invention will also become apparent from the following description of illustrative embodiments and the drawings. In this case, all the features described and/or depicted in themselves or in any combination form the subject matter of the invention, irrespective of the way in which they are grouped in the claims or the dependency references thereof.

In the drawings: shows a longitudinal section through a steam generating system according to the invention,

shows a cross section through a steam generating system according to the prior art,

shows a first cross section through a steam generating system according to the invention,

shows a second cross section through a steam generating system according to the invention.

Fig. 1 illustrates the steam generating system 1 , comprising the steam generator 2 and the steam drum 3 as principal components. The steam generator 2 is designed as a shell-and-tube evaporator and is set up horizontally. The hot synthesis gas 4 coming from a steam reforming reactor (not depicted) is introduced into the inlet chamber 5 of the steam generator 2, is distributed there between the tubes 6 of the tube bundle 13, flows onward into the outlet chamber 7 and leaves the steam generator 2 for further treatment or use (not shown). The steam drum 3 is arranged above the steam generator 2. The boiler feedwater 8 to be evaporated is fed into said steam drum. The water to be evaporated is circulated via the riser pipes 9 and the downpipes 10 in a natural circulation. The steam/water mixture entering the steam drum 3 via the riser pipes 9 is separated there, the steam 1 1 is dis- charged for further use and the water is fed back into the steam generator via the down- pipes 10. Here, the downpipes enter the jacket 12 of the steam generator 2 in the 0 o'clock position and then run past the heating tubes of the tube bundle 6 within the jacket 12 as far as the lower volume region of the jacket 12. The downpipes end as low as possible in the jacket to avoid steam bubbles getting into the downpipe and to achieve as large as possible a static head, i.e. as large as possible a vertical distance between the lower and the upper end of the downpipe, thereby assisting natural circulation.

Fig. 2 shows a cross section through a steam generating system with the downpipes 10' routed in accordance with the prior art. To increase clarity, the riser pipes have not been depicted, but, as in the example shown in Fig. 1 , they are once again arranged in the 0 o'clock position of the jacket 12. The downpipes 10' are connected to the steam drum 3 in the 4 and in the 8 o'clock position, run externally around the steam generator 2 and likewise open in the steam generator jacket 12 in the 4 and the 8 o'clock position.

Fig. 3a shows a cross section through a steam generating system 1 with the downpipe 10 routed in accordance with the invention. The downpipe 10 is connected to the steam drum 3 in the 6 o'clock position and passes through the jacket 12 of the steam generator 2 in the 0 o'clock position. Within the jacket 12, the downpipe 10 runs around the tube bundle 13 as far as the volume region of the water jacket 12 situated thereunder.

Fig. 3b likewise shows a cross section through a steam generating system with the downpipe 10 routed in accordance with the invention. The downpipe 10 is likewise connected to the steam drum 3 in the 6 o'clock position and passes through the jacket 12 of the steam generator 2 in the 0 o'clock position. Within the jacket 12, the downpipe 10 passes through the tube bundle 13 to the volume region of the water jacket 12 situated thereunder.

Industrial applicability

The invention offers the possibility of embodying a steam generating system in a less expensive and more space-saving way, wherein the setup of the system can also be carried out more flexibly in relation to the upstream and downstream apparatus.

List of reference signs

1 steam generating system according to the invention

V steam generating system according to the prior art

2 steam generator

3 steam drum

4 synthesis gas

5 inlet chamber

6 heating tube

7 outlet chamber

8 boiler feedwater

9 riser pipe

10 downpipe

10' downpipe according to the prior art

11 steam

12 jacket of the steam generator

13 heating tube bundle