INSTALLATION AND METHOD FOR GENERATING ENERGY

Abstract: The invention relates to an installation for generating energy, comprising: i) a unit (3) for generating fresh steam in the pressure range of about 80 bar to about 200 bar; ii) at least one steam turbine (11) for stepwise expansion of steam in at least two steam turbine sections (12-14); and iii) at least one reheater unit (35) which is connected between the two steam turbine sections (12,13) for indirect reheating of expanded steam to 320-400 DEG C with fresh steam. The invention also relates to a method for generating energy, comprising the steps: of i) generating fresh steam in the pressure range of about 80 bar to 200 bar; ii) expanding the steam in stepwise manner; and iii) indirectly reheating expanded steam with fresh steam to 320-450 DEG C.

Description: INSTALLATION AND METHOD FOR GENERATING ENERGY The present invention relates to an installation and to a method for generating energy with a waste incineration plant ( ΙP)or biomass power plant. More particularly, wherein for generating energy fresh steam is used with an increased steam pressure but not with an increased steam temperature. Steam with such steam conditions (increased steam pressure at non- increased steam temperature) has the drawback that at the low pressure outlet of the turbine the prevailing moisture content is relatively high and is higher than the maximum permissible moisture content of about 12.5%. In ABB Review, no. 1, 1998, pages 15-22 a power plant is described with two IP lines which produce superheated steam (40 bar/400°C) , and a WIP line which produces saturated steam (20 bar/230°C) . The superheated steam and the saturated steam are expanded in a steam turbine to form wet steam of 5 bar. At this low pressure wet steam is dried by reheating, thus enabling further expansion without excessive moisture formation. Reheating is used for steam drying and not for efficiency improvement . US-A-5, 457, 721 describes a nuclear installation for energy generation. High-pressure steam is mixed with saturated wet steam from the nuclear installation. Further expansion of the drier steam mixture is then possible . FR-A-2, 116, 671 describes a nuclear installation wherein saturated steam (35-60 bar/250-300°C) is fully expanded after steam drying with steam from the PWR. Reheating is not applied in any of the publications to improve the (electrical) efficiency. The present invention has for its object to obtain an efficiency improvement in WIPs and biomass power plants by making use of reheating at increased boiler pressure. The present invention is based on the insight that by reheating partially expanded steam (in particular intermediate pressure steam) not only is the moisture content decreased, but there also occurs an increase in efficiency. This is because during reheating with fresh steam the condensation heat can be used at the prevailing high temperature to reheat the steam to be expanded thereafter. The decrease in the moisture content which occurs is such that in the low pressure outlet of the turbine a moisture content prevails in the order of about 10%. The efficiency improvement is in the order of 3% points, for instance from 22% to 25% net efficiency. The present invention therefore provides an installation for generating energy, comprising: i. a unit for generating fresh steam in the pressure of about 80 bar to about 200 bar; ii. at least one steam turbine for stepwise expansion of steam in at least two steam turbine sections; and iii. at least one reheater unit which is connected between the two steam turbine sections for indirect reheating of expanded steam to 320-450°C with fresh steam. The invention also provides a method for generating energy, comprising the steps of: i. generating fresh steam in the pressure range of about 80 bar to 200 bar; ii. expanding the steam in stepwise manner; and iii. indirectly reheating expanded steam. The used fresh steam at increased pressure can be saturated or superheated. At a pressure of 80 bar a steam temperature is possible of 295°C (saturated) to 380°C (superheated) ; at 200 bar a temperature of 365°C to 550°C. The pressure/temperature range lies preferably between 90 bar/390°C and 150 bar/500°C. A characteristic pressure/temperature for a waste incineration plant (WIP) amounts to 100 bar/400°C. If in further preference an installation comprises a second incineration unit with a flue gas side heat exchanger for superheating the fresh steam to about 550 °C, it is possible to superheat the fresh steam to a relatively high steam temperature, whereby the energy efficiency increases further and the moisture content after expansion decreases further. An advantageous incineration unit comprises an exhaust gas boiler with a reactor for incineration and/or gasification. The indirect reheating using the reheater unit is partly dependent on the pressure/temperature conditions of the fresh steam. Reheating of the steam generally takes place up to a temperature in the range of 320 -450 °C. This lower limit is lower when reheating is applied at lower pressure. Pressures of 5-80 bar, preferably 10-40 bar, such as 15-30 bar are possible. The condensate formed in the installation during reheating with fresh steam can be reused to generate fresh steam and is fed back for this purpose to the unit for generating fresh stem. An optimal water balance thus results. The above stated method also includes the above mentioned preferred aspects. Mentioned and other features of the installation and method for generating energy while applying reheating of expanded steam will be further elucidated hereinbelow on the basis of two embodiments, which are given only by way of example without the invention being deemed limited thereto. Reference is made herein to the annexed drawings, in which: Figures 1 and 2 each show a schematic view of an installation for generating energy while applying reheating of expanded steam. Figure 1 shows an installation 1 for generating energy. Installation 1 comprises a waste incineration plant with an incineration unit 2 and a steam boiler 3. In incineration unit 2 domestic and/or industrial waste 4 is incinerated using air to pot-ash and hot flue gas 7. With this flue gas 7 fresh steam is generated in steam boiler 3 and cold flue gas is discharged via conduit 8 to chimney 9. The fresh steam is fed via conduit 10 to a steam turbine 11, which comprises turbine sections 12-14 which drive a generator 16 via a common turbine shaft 15. Instead of one steam turbine 11 with three turbine sections, use can also be made of a number of different steam turbines for stepwise expansion of steam. The fresh steam (100 bar/400°C) is expanded in turbine section 12 to 20 bar and guided via line 17 through a reheater unit 18, in this case a heat exchanger 18. This intermediate pressure steam is reheated in reheater unit 18 against fresh steam which is likewise fed to reheater unit 18 via line 19 and leaves this unit via line 20 as condensate which is then degassed in degasser 21 and fed back via pump 22 and conduit 23 to steam boiler 3. The condensate in line 20 has a temperature of 306°C. The reheated steam is fed via conduit 24 to the turbine section 13 and, after expansion, via conduit 25 to turbine section 14. A part of the expanded steam is fed via line 26 to degasser 21. The expanded steam which results in turbine section 14 (condenser pressure 80 mbar) passes through the heat exchanger 27, condenses and is fed via a pump 28 to degasser 21 (pressure 10.5 bar/temperature 150°C) . The degasser operates at a pressure of 10 bar. The feed water (105 bar/182°C) is then fed back via conduit 23 to steam boiler 3. Compared to an energy generating installation without reheating, an electrical efficiency improvement is realized of more than 2% points. Figure 2 shows an installation 29 according to the invention in which in addition to the incineration unit 2 a fluidized bed incineration unit 30 is applied which is connected to chimney 9 via the flue gas duct 31 passing through an exhaust gas boiler 39. Accommodated in exhaust gas boiler 39 is a heat exchanger 32 for superheating fresh steam formed in steam boiler 3 and steam formed in heat exchanger 40 which are supplied via line 33 and 41. Superheating takes place to a temperature of 520°C. Via line 34 steam is fed to the first turbine section 12 of steam turbine 11 and expanded. The expanded intermediate pressure steam is reheated in heat exchanger 35 and subsequently fed to turbine section 13 via conduit 36. The condensate formed from the superheated steam is fed via conduit 37 to degasser 21, to which a part of the expanded steam from turbine section 13 is also fed via conduit 38. The condensate has a temperature of about 306°C. From the degasser feed water is fed back via pump 22 and conduit 23 to steam boiler 3 and via line 42 to heat exchanger 40 of exhaust gas boiler 39.

Claims: CLAIMS 1. Installation for generating energy, comprising: i. a unit for generating fresh steam in the pressure range of about 80 bar to about 200 bar; ii. at least one steam turbine for stepwise expansion of steam in at least two steam turbine sections; and iii. at least one reheater unit which is connected between the two steam turbine sections for indirect reheating of expanded steam to 320-400°C with at least a part of the fresh steam. 2. Installation as claimed in claim 1, wherein the fresh steam has a temperature of 295°C (saturated) to 380°C (superheated steam) at 80 bar and 365°C (saturated) to 550°C (superheated steam) at 200 bar. 3. Installation as claimed in claim 2, comprising an incineration unit with a flue gas side heat exchanger for superheating the fresh steam to about 550°C. 4. Installation as claimed in claim 3, wherein the incineration unit comprises an exhaust gas boiler with fluidized bed incineration or gasification. 5. Installation as claimed in claims 1-4, wherein the reheater unit indirectly reheats the expanded steam to a temperature in the range of 320-450°C and a pressure of 5 to 80 bar. 6. Installation as claimed in claims 1-5, wherein condensate formed from fresh steam used for reheating is fed back to the unit to generate fresh steam. 7. Method for generating energy, comprising the steps of : i. generating fresh steam in the pressure range of about 80 bar to 200 bar; ii. expanding the steam in stepwise manner; and iii. indirectly reheating expanded steam with fresh steam to 320-450°C. 8. Method as claimed in claim 7, wherein the steam is reheated to a temperature of 320-450°C at a pressure of 5-80 bar. 9. Method as claimed in claim 7 or 8 , wherein the generated fresh steam is superheated to 550°C. 10. Method as claimed in claims 7-8, wherein condensate formed from fresh steam used for reheating is used to generate fresh steam.

Inventors: DE VRIES RONALD, MIDDELKAMP HUGO JOHAN, PLOUMEN PIETER JOSEPH, DE VRIES, RONALD, MIDDELKAMP, HUGO, JOHAN, PLOUMEN, PIETER, JOSEPH
Applicants: KEMA NV, MIDDELKAMP HUGO JOHAN, PLOUMEN PIETER JOSEPH, VRIES RONALD DE, DE VRIES, RONALD, MIDDELKAMP, HUGO, JOHAN, N.V. KEMA, PLOUMEN, PIETER, JOSEPH
Application year: 2001
Main classification: F01K7
IPC codes: F01K3, F01K7