l l l l l l l Il l l l l l l mlu?lul l l?l l l l l l 5,776,413 llllllll United States Patent 119] Kamberger et a1.  Patent Number:  Date of Patent:  CHEMICAL MODE OF OPERATION OF A WATER/STEAM CYCLE 3,415,692  Inventors: Werner Kamberger. Ober-Ohringen. Switzerland; Erhard Liebig, Ditzingen. Germany  Appl. N0.: 743,181  [DE] Germany ...................... .. 195 44 224.5 F02G 1/00  US. Cl. ........................ .. 422”; 60/39182; 60139.53;  Field of Search ............................ .. 422/7 ; 6059.182. 122/460; 122/472; 122/488 60/3953; 122/460. 472. 488; 203/10 References Cited U.S. PATENT DOCUMENTS 2,727,069 2,947,686 3,162,550 290/4011 4,693,213 9/1987 Yanai et al. ........................... .. 122/7 R 4,753,311 7/1988 Pagani et 31.. 60/3912 2/1988 4/1988 2/1989 3/1995 Germany . Germany . Germany . United Kingdom . Mathis. L.L.P. Int. Cl.6 ............................. .. C23F 11/00; F02C 6/00;  7/1978 Foster-Pegg .. Primary Examiner—Nina Bhat Attorney, Agent, or Firm—Burns. Doane. Swecker & Nov. 5, 1996 Foreign Application Priority Data Nov. 28, 1995 6/1977 Martz et al. .... .. 4,099,374 3627344A1 3635411A1 3724947A1 2281742 Switzerland  12/1968 Armentano ........................... .. 143/614 4,031,404 FOREIGN PATENT DOCUMENTS  Assignee: Asea Brown Boveri AG. Baden.  Filed: Jul. 7, 1998 12/1955 Van Waes ............................... .. 260/55 8/1960 Phillips. Jr,  ABSTRACT A multi-pressure waste-heat boiler (7) comprises at least one circulation steam generator, having a low-pressure econo mizer (15), a low-pressure drum (17) and a low-pressure evaporator (16), and at least one once-through steam gen erator having a high-pressure economiz/er (21). a high pressure evaporator (22) and a high-pressure superheater (23). An oxygen addition (32) is arranged between the steam drum (17) of the circulation steam generator and the high pressure economizer (21) of the once-through steam gen erator. An ammonia addition (31) is arranged in the feed line (33) leading to the circulation steam generator. 208/340 12/1964 Dvoracek etal, ................... .. 148/614 2 Claims, 1 Drawing Sheet US. Patent 5,776,413 Jul. 7, 1998 Wwt N v _ m mmIND/M .m,. I N bmm9 X x Q ? x \QQ\“I. . % Iiq mu3mmaa.l2 ‘?umQ3 l/[email protected] e3M[9v aR m_m wt \H. ~ mm . T1 m hm TN 5.776.413 1 2 CHEMICAL MODE OF OPERATION OF A WATER/STEAM CYCLE FIG. 2 is a graph showing oxygen concentration versus ammonia concentration of condensate X. steam Y. and high pressure feedwater Z for the method of the invention in comparison with conventional methods. BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a multi-pressure waste-heat boiler having at least one circulation steam generator. essentially DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings. wherein like reference comprising a low-pressure economizer. a low-pressure drum and a low-pressure evaporator. and at least one once-through numerals designate identical or corresponding parts throughout the several views. only the elements required for steam generator. essentially comprising a high-pressure understanding the invention are shown. and the direction of ?ow of the working media is shown by arrows. in FIG. 1 economizer. a high~pressure evaporator and a high-pressure superheater. It also relates to a method of operating such a fresh air drawn in via a line 1 is compressed in a compressor plant. 2 to me working pressure in the gas-turbine system. The compressed air is greatly heated in a combustion chamber 3. ?red for example with natural gas. and the fuel gas thus developed is expanded in a gas turbine 4 to perform work. 2. Discussion of Background Waste-heat boilers for utilizing the waste heat of energy or process plants producing hot gas are designed either as circulation boilers with drum or else as once-through forced ?ow boilers. The chemical mode of operation corresponds to the conventional speci?cations for conventional steam 20 The energy obtained in the process is delivered to a gen erator 5 or the compressor 2. The still hot exhaust gas from the gas turbine is fed via a line 6 from the outlet of the gas generating plants (e.g. TRD 611. VGB-R 450 L. EPRI Guidelines). The alkaline mode of operation. the neutral turbine to a waste-heat steam-generating plant 7 and is passed from there. after delivery of its heat. into the open via mode of operation and the combined mode of operation. as used without exception. are brie?y explained in FIG. 2 to be a line 8 and a ?ue (not shown). In the water/steam cycle. a three- stage steam turbine 9. 10 and 11 is arranged on the same shaft as the gas turbine. The described later. Problems arise if a waste-heat boiler is 25 equipped with a circulation low-pressure system and a working steam expanded in the low-pressure turbine 11 once-through high-pressure system. If. for example. the condenses in a condenser 13. The condensate is delivered directly into the steam generator 7 by means of a condensate conventional alkaline mode of operation is used. the ammonia. on account of its ditferent solubility in steam and water. increases in concentration in the steam region of the low-pressure drum. Inside the drum. the ammonia content is pump 14. It is remarkable that the plant has no low-pressure 30 heated as a rule by bleed steam. then disproportionately high in the steam and accordingly The waste-heat steam-generating plant 7 is constructed as too low in the water. If the once-through steam generator is now fed with water from the low-pressure drum. its exchange surfaces are insu?iciently protected against cor rosion and sediments. since no optimum oxide protection an upright boiler and in the present case works according to 35 ?lm can build up. SUMMARY OF THE INVENTION Accordingly. one object of the invention is to provide a novel plant and an operating method of the type mentioned at the beginning in which all parts of the plant can be protected against corrosion and the formation of sediments. This is achieved according to the invention in that an oxygen addition is arranged between the low-pressure drum of the circulation steam generator and the high-pressure economizer of the once-through steam generator. and in that an ammonia addition is arranged in the condensate line leading to the circulation steam generator. A method of operating such a plant is distinguished by the 45 could also be used. The low-pressure system is constructed as a circulation system with drum. in which case a forced circulation system has been selected here. In the ?uegas path of the boiler. it consists of a low-pressure economizer 15 into which the condensate is directed. a low-pressure evaporator 16. and a connected to a drum 17 via a circulating pump 18. The superheated steam is transferred via a low-pressure steam line 28 into a suitable stage of the intermediate-pressure steam turbine 10. The high-pressure system is constructed as a once through forced_flow system and can thus be designed for 50 55 both subcritical and supercritical parameters. In the ?ue-gas path of the boiler. it essentially comprises the high-pressure economizer 21. the high-pressure evaporator 22 and the high-pressure superheater 23. The working medium is fed to the high-pressure economizer 21 from the low-pressure drum 17 via a high-pressure feedpump 20. In this way. the hitherto conventional feedwater tank can be dispensed with. The superheated steam is transferred via a livesteam line 24 into the high-pressure part 9 of the steam turbine. For the phase separation. a separator 25 is provided into which the discharge of the high-pressure evaporator 22 leads. At its top end. the separator is connected to the high-pressure superheater 23. At its bottom end. it is addi BRIEF DESCRIPTION OF THE DRAWINGS tionally provided with a sludge drain line 29. Arecirculation A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained line 26 likewise branches oil‘ from the bottom end of the separator. which recirculation line 26 contains a shut-01f as the same becomes better understood by reference to the following detailed description when considered in connec tion with the accompanying drawings FIG. 1 is a schematic representation of a combined gas/steam power station plant. a dual-pressure steam process. Of course. a horizontal boiler low-pressure superheater 19. The low-pressure evaporator is fact that so much ammonia solution is added in a dosed quantity to the condensate. which has a pH value between 8.8 and 9.4. that a pH value between 9.4 and 9.7 is reached in the steam phase of the low-pressure drum. and in that so much gaseous oxygen is introduced into the water ?owing to the once-through steam generator that its oxygen content ranges between 50 and 150 ppb at a pH value between 8.8 and 9.2. preheaters. feedwater tanks and high-pressure preheaters 65 member 30 and leads into the low-pressure drum 17. After the partial expansion in the high-pressure part 9 of the turbine. the steam is reheated before transfer into the 5,776,413 3 4 intermediate-pressure turbine 10. In the example. this reheating is effected in heat-exchange surfaces 27 which are arranged in the ?ue-gas path of the steam generator above from oxygen pressure bottles or from an existing oxygen gas network. and the ammonia addition may be effected in the form of diluted ammonia solution by means of dosing pumps. The novel mode of operation can be recognized in the diagram in FIG. 2. The pH value is plotted on the abscissa and the oxygen content in [ppb] is plotted on the ordinate. The three dotted regions in each case represent the conven tional modes of operation mentioned at the beginning; namely A the neutral mode of operation. 2 the combined mode of operation and C the alkaline mode of the operation. The novel mode of operation is shown in the shaded regions. The initial position is the region X. which represents the oxygen content and the pH value of the condensate after the ammonia dosing at the boiler inlet. Region Y shows the state of the low-pressure steam enriched with ammonia. and region Z shows that of the high-pressure feedwater enriched the high-pressure superheater 23. By variation of the pressures and mass flows in the circulation system and in the once-through system. a wide range of combined processes can be covered with such a steam generator. In the case of the plant working by the variable-pressure method. a boiler having a division of the mass ?ows in the low-pressure system and the high-pressure system in a ratio of 1:4 or 1:5 is considered to be appropriate. The steam production starts in the boiler when the respec tive temperatures of ebullition are reached. The initial steam in the low-pressure system is generated by expansion of recirculated high-pressure saturated water from the separa tor. The separator ensures that the high-pressure superheater remains dry at all times during normal operation and steam superheated in good time is available at the boiler outlet. It is apparent from FIG. 1 that a condensate-purifying plant is dispensed with. Underlying this fact is the idea that the contaminants in the steam/water cycle can be drawn off in the region of the separator. The purifying of the stearn/ with oxygen. The result of the separate addition of ammonia (31) upstream of the low-pressure drum 17. preferably into the feed line 33 downstream of the condensate pump 14. and of oxygen (32) downstream of the low-pressure drum 17. preferably upstream of the high-pressure feedpump 20. is 25 water cycle can be etfected at both full load and part load. To this end. the high-pressure system is overfed. Le. a larger quantity of water than necessary is delivered through the once-through steam generator via the high-pressure feed pump. It goes without saying that the high-pressure feed pump has to be of correspondingly larger design for the extra quantity. The delivered water quantity is set in such a way that wet steam passes into the separator in any case. The contaminants are bound in the water droplets of the water! steam mixture. The water portion of the steam is separated in the separator by suitable means and drawn o? via the 30 35 sludge drain line 29. Of advantage in this method is the fact According to the invention. measures are now to be taken in order to reduce the susceptibility to corrosion mentioned at the beginning in such boilers. in particular in the once through steam generator. To this end. a novel chemical mode evaporator. but not for the formation of a proper oxide protection ?lm on the once-through mbing. which is fed with the same drum water. In order to now create ideal protective ?lm conditions here. so much gaseous oxygen 32 is fed into the feedwater ?owing to the high-pressure economizer that an oxygen content between 50 and 150 ppb becomes estab lished. The apparatus for this method is extremely simple. The oxygen addition 32 may be elfected volumetrically directly wise than as speci?cally described herein. What is claimed as new and desired to be secured by Letters Patent of the United States is: l. A method of operating a multi-pressure waste-heat boiler having at least one circulation steam generator includ ing a low-pressure eoonomizer. a low-pressure drum and a low-pressure evaporator. and at least one once-through steam generator. including a high-pressure economizer. a the method comprising the steps of: 45 50 via the low-pressure economizer 15. The result of the different solubility is that the ammonia increases in concen tration in the steam. If. for example. the pH value of the water is still 9.25 upon entering the drum. the pH value in concentration. whereas the drum water only has a pH value of 9.0. This value is sufficient for the requirements of the LP quantity of conditioning chemicals. the vacuum degassing in the condenser. and the desalting. described in connection with the purifying of the cycle. from the separator 25. Obviously. numerous modi?cations and variations of the present invention are possible in light of the above teach ings. It is therefore to be understood that within the scope of high-pressure evaporator and a high-pressure superheater. of operation having the following method steps is selected: the steam increases to about 9.6 as a result of the increase in speci?ed water/steam quality is regulated via the dosed the appended claims. the invention may be practiced other that contaminants are largely removed from the cycle even after a few passes. i.e. within the shortest time. Downstream of the condenser 13. the condensate as a rule has an oxygen content 60 ppb and a pH value between 8.8 and 9.4. So much ammonia solution is now introduced into this condensate by means of a dosing unit that it has a pH value between 9.1 and 9.4 in the feed line to the boiler. The water passes with this value into the low-pressure drum 17 that all parts of the plant are e?ectively protected. The introducing an amount of dissolved ammonia into con densate ?owing into the circulation steam generator. said condensate having a pH value between 8.8 and 9.4. su?icient to obtain a pH of steam in the steam space of the low-pressure drum at a value between 9.4 and 9.7. and introducing an amount of gaseous oxygen into water ?owing to the once-through steam generator su?icient to obtain an oxygen content in a range between 50 and 55 150 ppb at a pH value between 8.8 and 9.2. 2. A multi-pressure waste-heat boiler comprising at least one circulation steam generatorincluding a low-pressure economizer. a low-pressure drum and a low-pressure evaporator. and at least one once-through steam generator. including a high-pressure economizer fed by a line from the low-pressure drum. a high-pressure evaporator and a high pressure superheater. means for introducing oxygen in the line between the low-pressure drum of the circulation steam generator and the high-pressure economizer of the once through steam generator and means for introducing ammo nia in a feed line leading to the circulation steam generator.
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