# US 9,518,481 B2 · Method for operating a recirculating waste heat steam generator > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,518,481 B2 - Document ID: US9518481B2 - Status: Granted - Kind: B2 - Application number: 14/123,418 - Filed: 2012-05-23 - Published: 2014-04-24 - Granted: 2016-12-13 - Earliest claimed: 2011-06-06 - Assignees: Siemens Aktiengesellschaft - Applicants: Jan Bruckner; Martin Effert; Frank Thomas - Inventors: Jan Bruckner; Martin Effert; Frank Thomas - Web page: https://patentgrep.com/patent/US9518481B2 ## CPC - F01K 23/108: {Regulating means specially adapted therefor} - F01K 23/101: {Regulating means specially adapted therefor (F01K23/105, F01K23/108 take precedence)} - F22B 1/1815: {using the exhaust gases of gas-turbines} - F22B 35/02: for steam boilers with natural convection circulation - F01K 23/10: with exhaust fluid of one cycle heating the fluid in another cycle (F01K17/025 takes precedence) - F22D 5/26: Automatic feed-control systems - Y02E 20/16: Combined cycle power plant [CCPP], or combined cycle gas turbine [CCGT] - Y02P 80/15: On-site combined power, heat or cool generation or distribution, e.g. combined heat and power [CHP] supply - F01K: STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES (gas-turbine or jet-propulsion plants F02; nuclear power plants, engine arrangements therein G21D) - F22B: METHODS OF STEAM GENERATION; STEAM BOILERS - F22D: PREHEATING, OR ACCUMULATING PREHEATED, FEED-WATER FOR STEAM GENERATION; FEED-WATER SUPPLY FOR STEAM GENERATION; CONTROLLING WATER LEVEL FOR STEAM GENERATION; AUXILIARY DEVICES FOR PROMOTING WATER CIRCULATION WITHIN STEAM BOILERS - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION - Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS ## Abstract A method for operating a recirculating waste heat steam generator is provided, in which in a pressure stage of the recirculating waste heat steam generator, the feed water mass flow is guided on the basis of a specified desired value in order to control the water level in a drum. The method should give a recirculating waste heat steam generator a particularly high degree of efficiency and simultaneously a particularly high level of operational flexibility. For this purpose the thermal input introduced into an evaporator of the pressure stage is used as input variable in the determination of the desired value. ## Claims ### Claim 1 A method for operating a recirculating waste heat steam generator comprising, determining a specified desired value, managing the feedwater mass flow in a pressure stage of the recirculating waste heat steam generator on the basis of the specified desired value in order to control the water level in a drum, wherein the thermal power introduced into an evaporator of the pressure stage is used as an input variable in the determination of the desired value, wherein, in the determination of the thermal power introduced into the evaporator of the pressure stage, a flue gas mass flow and a difference in the specific enthalpy of the flue gas at an inlet and outlet of the evaporator of the pressure stage are used, and wherein, in the determination of the specific enthalpy of the flue gas at the outlet of the evaporator, a saturation temperature of the flow medium is used as an input variable. ### Claim 2 (depends on 1) The method as claimed in claim 1, wherein the specific enthalpy of the flue gas at the inlet of the evaporator of the pressure stage is used with a time delay. ### Claim 3 (depends on 1) The method as claimed in claim 1, wherein an enthalpy difference of the flow medium between the inlet and the outlet of the evaporator of the pressure stage is used as an input variable in the determination of the desired value. ### Claim 4 (depends on 1) The method as claimed in claim 1, wherein a time-delayed saturation temperature of the flow medium in the pressure stage is used as an input variable in the determination of the desired value. ### Claim 5 (depends on 1) The method as claimed in claim 1, wherein a time-delayed density of the flow medium in the pressure stage is used as an input variable in the determination of the desired value. ### Claim 6 (depends on 1) A recirculating waste heat steam generator adapted to carry out the method as claimed in claim 1. ### Claim 7 (depends on 6) A gas and steam turbine power plant with a recirculating waste heat steam generator as claimed in claim 6. ### Claim 8 (depends on 1) The method as claimed in claim 1, wherein, in the determination of the specific enthalpy of the flue gas at the inlet of the evaporator of the pressure stage, a temperature of the flue gas at the inlet of the evaporator of the pressure stage is used as an input variable. ### Claim 9 (depends on 8) The method as claimed in claim 8, wherein, in the determination of the temperature of the flue gas at the inlet of the evaporator of the pressure stage, a flue gas temperature at a flue gas inlet of the recirculating waste heat steam generator that is located upstream of the inlet of the evaporator is used as a basis to estimate the temperature of the flue gas at the inlet of the evaporator of the pressure stage. ### Claim 10 (depends on 9) The method as claimed in claim 9, wherein the flue gas temperature at a flue gas inlet of the recirculating waste heat steam generator is used together with a predetermined parameter map to estimate the temperature of the flue gas at the inlet of the evaporator of the pressure stage. ### Claim 11 A method for operating a recirculating waste heat steam generator comprising, determining a specified desired value, managing the feedwater mass flow in a pressure stage of the recirculating waste heat steam generator on the basis of the specified desired value in order to control the water level in a drum, wherein the thermal power introduced into an evaporator of the pressure stage is used as an input variable in the determination of the desired value, and wherein a time-delayed saturation temperature of the flow medium in the pressure stage is used as an input variable in the determination of the desired value. ### Claim 12 (depends on 11) The method as claimed in claim 11, wherein the time-delayed saturation temperature of the flow medium in the pressure stage is of the flow medium at an outlet of the evaporator. ### Claim 13 (depends on 11) The method as claimed in claim 11, wherein, in the determination of the thermal power introduced into the evaporator of the pressure stage, a flue gas mass flow and a difference in the specific enthalpy of the flue gas at an inlet and outlet of the evaporator of the pressure stage are used, and wherein, in the determination of the specific enthalpy of the flue gas at an inlet of the evaporator of the pressure stage, a temperature of the flue gas at the inlet of the evaporator of the pressure stage is used as an input variable. ### Claim 14 A method for operating a recirculating waste heat steam generator comprising, determining a specified desired value, managing the feedwater mass flow in a pressure stage of the recirculating waste heat steam generator on the basis of the specified desired value in order to control the water level in a drum, wherein the thermal power introduced into an evaporator of the pressure stage is used as an input variable in the determination of the desired value, and wherein a time-delayed density of the flow medium in the pressure stage is used as an input variable in the determination of the desired value. ### Claim 15 (depends on 14) The method as claimed in claim 14, wherein the time-delayed density is of the flow medium at one or both of an inlet and an outlet of an economizer of the recirculating waste heat steam generator. ### Claim 16 (depends on 14) The method as claimed in claim 14, wherein, in the determination of the thermal power introduced into the evaporator of the pressure stage, a flue gas mass flow and a difference in the specific enthalpy of the flue gas at an inlet and outlet of the evaporator of the pressure stage are used, and wherein, in the determination of the specific enthalpy of the flue gas at the outlet of the evaporator, a saturation temperature of the flow medium is used as an input variable. ### Claim 17 (depends on 14) The method as claimed in claim 14, wherein, in the determination of the thermal power introduced into the evaporator of the pressure stage, a flue gas mass flow and a difference in the specific enthalpy of the flue gas at an inlet and outlet of the evaporator of the pressure stage are used, and wherein, in the determination of the specific enthalpy of the flue gas at the inlet of the evaporator of the pressure stage, a temperature of the flue gas at the inlet of the evaporator of the pressure stage is used as an input variable.