ITMI990634A1 - STEAM GENERATOR WITH IMPROVED FUNCTIONALITY - Google Patents

Description

DESCRIPTION

The present invention refers to a steam generator fed by oil and / or gas, having improved functionality. In particular, the present invention relates to a steam generator characterized in that it comprises superheater devices having a particular structure and positioning.

It is known from the state of the art that steam generators fed with oil and / or gas have a structure similar to that schematically presented in figure 1.

The steam generator or boiler, indicated by the reference number 1, has a chamber 2, in which the combustion takes place, schematically indicated by a dashed circular line, of the fuel injected through a system of nozzles (not shown in the figure).

The fumes generated by combustion, indicated schematically by the dashed arrow 3, follow a path that allows them to exchange heat with superheater devices according to the steam heating cycle of the plant.

The heating of the steam inside the superheater devices can take place either by direct radiation from the combustion chamber 2 or by the intertubular cavities, or by convective exchange with the outgoing fumes.

The superheater devices will be described in more detail below. They are positioned both in the area indicated by the reference number 100, defined with the technical term "first step area" of the fumes leaving the boiler, and in the area indicated by the reference number 101, defined with the technical term "zone second step "of the fumes leaving the boiler.

To ensure a correct supply of heat to said superheater devices, the recirculation of a portion of the fumes leaving the boiler is provided. Thanks to the action of fans, a portion of the fumes leaving the boiler is re-introduced, as schematically indicated by the dashed arrow 5, into the combustion chamber 2.

The steam generator 1 provides for a steam superheating cycle which comprises a cylindrical body 6 positioned on the top of the boiler and containing water and steam, in saturated steam conditions at the operating pressure of the steam cycle.

The water contained in the cylindrical body 6, through a system of drop pipes not indicated in figure 1, is conveyed, as indicated schematically by the arrow 8, to a system of collectors 9. From the system of collectors 9, the water reaches a series of pipes 90, partially illustrated in Figure 1, arranged along the wall of the combustion chamber 2. In correspondence with the pipes 90, the water is heated by the effect of the thermal flow coming from the combustion and is sent again in the form of a mixture water-steam to the cylindrical body 6 (arrow 10).

The cylindrical body 6 comprises a series of water-steam separators which convey (arrow 11) the steam to a first superheating device 12, positioned at the outlet of the chamber 2 and indicated by the technical term "platen". From the device 12 the steam reaches (arrow 120) a manifold 13 which feeds the boiler ceiling.

The steam then flows (arrow 130), through a series of pipes arranged along the wall 131 of the boiler until it reaches (arrow 15) a second superheater device indicated globally by the reference number 14. The superheater device 14 is indicated by the technical term of "SH1" (Super Heater 1) and is positioned in a region of the boiler where the fumes take on a suitable temperature, in this case at the top of the boiler. The device SH1 14 is divided into a steam inlet bank 16 located in correspondence with the second pass area of the fumes and in a steam outlet bank 17 located in correspondence with the first pass zone. The superheated steam is conveyed (arrow 18) to a third superheater device 19 indicated with the technical term "SH2" (Super Heater 2). The SH2 device 19 is positioned downstream of the platen 12. The steam leaving the SH2 device is sent (arrow 190) to a first stage of a steam turbine 20 defined by the technical term of "HPT" (High Pressure Turbine). The steam at reduced pressure and temperature, leaving the HPT stage after a first expansion phase, returns to the boiler (arrow 21) in a fourth superheater device 22 defined with the technical term "RH" (Re-Heater). In the RH device, the steam is again superheated and conveyed (arrow 23) to a second stage of the steam turbine 24, defined by the technical term of "IPT" (Intermediate Pressure Turbine). After the complete expansion process in the turbine, the steam close to saturation is sent (arrow 25) to a condenser (not shown in the figure) where the condensation phase takes place. From the condenser the water reaches the device 26 (detectable "economizer") where it undergoes a new heating before being sent to the cylindrical body 6 (arrow 10).

Figure 2 shows in greater detail the superheater devices described in Figure 1. Each superheater device consists of one or more series of bundles of pipes connected together.

Among the various superheater devices there are blowers 27 used for cleaning the bundles of tubes, through the injection at high pressure of steam. There are also access doors 28 used for inspection of the tube bundles constituting the superheater devices.

The steam generator described in Figure 1, while fulfilling the intended task, has some drawbacks.

In particular, the control of the steam heating, operated by the RH device 22. The heat input to the RH device is in fact mainly due to convective heat exchange with the fumes passing through the first step area of the steam generator. Moving away from the combustion chamber 2, therefore, the overall heat input to the RH device decreases due to the decrease in the smoke-steam temperature difference. Furthermore, as the load decreases, the percentage of heat due to convective heat exchange decreases. This requires a relatively high power of the fans for the recirculation of the fumes in the boiler, in order to have a satisfactory supply of heat to the RH device. It is therefore evident that a stable regulation of the steam heating in the RH device is difficult and burdensome as it depends on numerous factors whose control is complex.

In the described configuration, moreover, there are intertubular cavities and a high number of blowers and inspection doors, in particular between the RH and SH2 devices with a consequent increase in overall dimensions.

The aim of the present invention is to provide a steam generator which allows to obtain a considerable improvement in the steam superheating process, in particular by the RH device.

Within this aim, an object of the present invention is to provide a steam generator which allows to obtain an easier regulation of the temperature of the steam leaving the device RH as the load varies.

Another object of the present invention is to provide a steam generator which allows to reduce the power required of the fans for recirculation of the fumes in the boiler.

A further object of the present invention is to provide a steam generator which has reduced overall dimensions.

Another object of the present invention is to provide a steam generator which has a reduced number of blowers and access doors for inspection of the tube bundles.

Not least object of the present invention is to provide a steam generator which is easy to manufacture and highly reliable.

This task and the aforementioned purposes, as well as other purposes which will become clearer in the following, are achieved by a steam generator comprising:

- a cylindrical body and relative water and steam separators, - a first superheater device (platen) connected to said cylindrical body, said first superheater device receiving the steam coming out of said cylindrical body and being positioned near the combustion chamber of said steam generator;

- a second superheater device (SH1) connected to said first superheater device, said second superheater device receiving the steam output from said first superheater device and being positioned near the boiler top of said steam generator;

- a third superheater device (SH2) connected to said second superheater device, said third superheater device receiving inlet the steam leaving said second superheater device and introducing the superheated steam into a first steam turbine stage;

- a fourth superheater device (RH) which receives the steam leaving said first steam turbine stage and introduces the superheated steam into a second steam turbine stage;

characterized in that said fourth superheater device (RH) is positioned, with reference to the direction of motion of the fumes in said steam generator, downstream of said first superheater device and upstream of said third and second superheater devices, respectively.

Further characteristics and advantages of the invention will become clearer from the description of a preferred but not exclusive embodiment of the steam generator according to the invention, illustrated by way of non-limiting example in the accompanying drawings and in which:

- figure 1 is a schematic view of a known type of steam generator;

Figure 2 represents in greater detail the superheater devices belonging to the steam generator illustrated in Figure 1;

figure 3 schematically represents a steam generator according to the invention.

With reference to Figure 3, the steam generator according to the invention is schematically presented, in which the elements corresponding to what has been described above are indicated with the same reference.

The steam generator according to the invention comprises a superheater device RH, indicated with 83, positioned, with reference to the direction of motion of the fumes 3 in the boiler, downstream of the platen superheater device 12 and upstream of the superheater devices SH280 and SH1 14, in the first pass area 100 of the fumes.

Preferably, the RH 83 device is positioned in the flue gas first pass area in such a way that there are no intertubular cavities between the RH 83 device and the SH280 device. For this purpose, the tube banks of said devices RH and SH2 are arranged adjacent to each other.

Conveniently, the RH 83 device is made in such a way as to present the steam inlet pipes, which receive the steam from the HPT turbine stage, positioned upstream with respect to the direction of motion of the fumes 3 in the boiler. The steam outlet pipes, communicating with the IPT turbine stage, are positioned downstream, so that the steam path along the RH 83 device is co-current with the direction of the fumes path 3 in the boiler.

The RH 83 device undergoes a greater thermal radiation since the fumes temperatures are higher in correspondence with the position assumed by the RH 83 device itself.

This fact considerably increases the percentage contribution of heat due to irradiation even at relatively low boiler loads and therefore allows to decrease the power required by the means for recirculating the fumes in the boiler.

The path of the steam in the RH 83 device, co-current with the motion of the fumes in the boiler, together with the absence of intertubular cavities between the RH 83 device and the SH280 device, allows for optimal management of the steam temperature in the RH 83 device. the steam coming from the HPT turbine stage, at a relatively low temperature (e.g. 350 ° C) following a first expansion, it is introduced into the RH device in correspondence with banks of pipes positioned in a relatively high temperature zone of the boiler while the steam leaving the RH device, at a relatively high temperature after the superheating process (e.g. 540 ° C), passes through banks of pipes positioned in an area of the boiler at a relatively low temperature.

This fact makes it possible to avoid excessive overheating of the tube banks of the RH 83 device, even though said device is positioned at a shorter distance from the combustion chamber of the boiler, compared to similar devices of the prior art.

The tube banks of the SH2 device also prevent the RH device from receiving excessive heat input from the intertubular cavities downstream of the RH device. Moreover, thanks to the absence of intertubular cavities, the overall dimensions are reduced since there are no blowers and inspection doors between the RH 83 device and the SH2 80 device.

The steam generator thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; furthermore, all the details can be replaced by other technically equivalent elements.

In practice, the materials employed, so long as they are compatible with the specific use, as well as the dimensions, may be any according to the requirements and the state of the art.

Claims (3)

CLAIMS 1. Steam generator comprising: - a cylindrical body and relative water and steam separators; - a first superheater device connected to said cylindrical body, said first superheater device receiving the steam leaving said cylindrical body and being positioned in proximity to the combustion chamber of said steam generator; - a second superheater device connected to said first superheater device, said second superheater device receiving the steam output from said first superheater device and being positioned near the boiler top of said steam generator; - a third superheater device connected to said second superheater device, said third superheater device receiving the steam coming out of said second superheater device at its inlet and introducing the superheated steam into a first steam turbine stage; - a fourth superheater device which receives the steam leaving said first steam turbine stage and introduces the superheated steam into a second steam turbine stage; characterized in that said fourth superheater device is positioned, with reference to the direction of motion of the fumes in said steam generator, downstream of said first superheater device and upstream of said third and second superheater devices respectively. 2. Steam generator according to claim 1 characterized in that said fourth superheater device has, with reference to the direction of motion of the fumes in said steam generator, banks of steam inlet pipes positioned upstream with respect to the banks of steam outlet pipes . 3. Steam generator according to one or more of the preceding claims, characterized in that the banks of tubes of said fourth superheater device are located adjacent to the banks of tubes of said third superheater device without intertubular cavities between said fourth superheater device and said third superheater device.