FR2645946A1 - Steam-raising plant with a fossil fuel-fired boiler and electric heater in a loop - Google Patents

Abstract

This steam-raising plant comprises a fossil fuel-fired boiler 1 with a heating body 4 receiving at its inlet water in the liquid phase and delivering, at its outlet, water in the vapour phase. According to the invention it further includes a heater 12 making it possible to: - take water up from inside the heating body at a level 10 where this water is in the liquid phase in a state which is close to its saturation point; - heat to saturation the water thus taken up using electric means 13 so as to bring about a partial vaporisation of this water, and - reintroduce into the heating body, under the water surface and at a level 15 which is above the take-up level, the mixture of liquid and vapour thus obtained. The mixture of liquid and vapour produced by the heater comprises at most 50% vapour, preferably between 10 and 20% vapour.

Description

 The present invention relates to a steam production installation comprising a fossil fuel boiler provided with auxiliary electric heating means.

 In mixed boilers of this type, it is important to optimize the respective use of the two types of energy so as to minimize the overall operating cost of the installation.

 The present invention provides such an optimized installation.

According to the invention, the steam production installation, which comprises a fossil fuel boiler with a heating body receiving water in the liquid phase and delivering water in the vapor phase, further comprises a heater allowing
- take water from inside the heating body at a level where it is in the liquid phase in a state close to its saturation point,
- heating the water to saturation thus withdrawn by electrical means so as to cause a partial vaporization thereof, and
- reintroduce into the heating body, under the water level and at a level higher than the sampling level, the mixture of liquid and vapor thus obtained.

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We will now give a description of an exemplary implementation of the invention, with reference to the single appended figure which schematically represents the installation for producing steam implementing the teachings of the present invention.

 The reference 1 designates the main boiler, which comprises a burner 2 supplied with fossil fuel by a pipe 3. The combustion makes it possible to raise the temperature of a heating body 4 supplied with cold water by the pipe 5 which opens out at the bottom of this heater. The steam is collected at the top of the boiler, above the water, by a pipe 6 leading to a distributor 7 allowing to feed several separate secondary pipes 8. A smoke tube 9 makes it possible to eliminate the combustion products .

 I1 is further provided a heater system which draws water from the heating body 4 at a point 10. The water thus withdrawn is directed through a line 11 to a heater 12 provided with an electrical resistance 13. The product of this heating is recycled by a pipe 14 inside the heating body 4, at a point 15 located below the level of the water body but at a level higher than that of the sampling point 10.

 Characteristically of the invention, the sampling point 10 is chosen so that the water that is withdrawn is still in the liquid phase but at saturation, that is to say at a point very close to the point vaporization, taking into account the temperature and pressure conditions prevailing at the sampling point.

 In this way, the electric heater will only have to provide the caloric intake corresponding to the latent heat of vaporization of water, without having to raise the temperature of the liquid phase to the vaporization temperature.

 For the overall performance of the installation to remain satisfactory, it is necessary that the vaporization is not complete, that is to say that the heater delivers at the outlet a mixture of liquid water and steam water, the proportion by mass of the vapor phase which must remain less than 50%. It has been found that the heat exchanges were the most satisfactory for a proportion of the vapor phase of between 10 and 20%.

 The water circulation in the loop of the heater can be a natural circulation (thermosyphon operation), or a forced circulation, with a pump inserted in the circuit; in the latter case, it will be necessary to use a pump with low differential pressure so as not to significantly modify the pressure of the water withdrawn.

Claims (4)

 1. A steam production installation comprising a fossil fuel boiler (1) with a heating body (4) receiving water in the liquid phase and delivering water in the vapor phase, characterized in that that it further comprises a heater (12) making it possible to  - take water from inside the heating body at a level (10) where it is in the liquid phase in a state close to its saturation point,  heating the water to saturation thus withdrawn by electrical means (13) so as to cause a partial vaporization of the latter, and  - reintroduce into the heating body, under the water level and at a level (15) higher than the sampling level, the mixture of liquid and vapor thus obtained.  2. The installation of claim 1, characterized in that the mixture of liquid and vapor produced by the heater contains at most 50%, by mass, of vapor.  3. The installation of claim 2, characterized in that the mixture of liquid and vapor produced by the heater comprises at most 20%, by mass, of vapor.  4. The installation of claim 1, characterized in that the mixture of liquid and vapor produced by the heater comprises at least 10%, by mass, of vapor.