Lünen State-of-the-Art 813MW Coal-Fired USC Boiler with High Efficiency and Flexibility

Transcription

1 Lünen State-of-the-Art 813MW Coal-Fired USC Boiler with High Efficiency and Flexibility Yuta Sato IHI Corporation Energy & Plant Operations Power-Gen Europe 2014, Cologne, Germany, 3-5 June, 2014 Track 4: Advanced & Flexible Steam Plants, Session 4: Large PC/CFB USC Steam Generators

2 Abstract In recent years, in terms of reducing CO2 emission and fuel cost savings, high plant efficiency is paramount requirement for the coal-fired power plant. Meanwhile, high flexibility is important challenge to follow the grid demand which changes suddenly and frequently by increasing the share of renewable energy in Europe. Coal-fired power plant Lünen 813MW owned by Trianel Kohlekraftwerk Lünen GmbH & Co. KG is based on the state-of-the-art technology to meet various requirements for high efficiency and flexibility. IHI was responsible for EPC contractor of the boiler and environmental equipment. In order to achieve high efficiency, IHI supplied USC (Ultra-Super Critical) boiler with main/reheat steam temperatures of 600/610degC and main steam pressure of 28.7MPa. For the further efficiency improvement, Parallel Pass Design is introduced for reheat steam temperature control. The gas passage is divided in two as reheater and superheater/economizer pass, and steam temperature is controlled by varying the ratio of gas flow without spray water injection. By introducing the above features and the state-of-the-art steam turbine, we successfully achieved 46% plant efficiency in LHV base and it was the world s highest class record in coal-fired power plant. In the performance test and the commissioning, we confirmed all guaranteed values; e.g. plant / boiler efficiency and emissions are fulfilled. For high flexibility, IHI applied Wide Range Burner which could expand operating range, and the minimum continuous operation load 25% with pure coal firing. The load could be reduced according to grid demand, when large amount of electricity generated by wind and solar power. Therefore, we could save the consumption of high-priced fuel oil since startup/shutdown becomes unnecessary due to this advantageous system. We successfully handed the plant over to this owner in July

3 1. Introduction Since coal is an energy source widely distributed throughout the world, its price is stable and there is a considerable amount deposited in reserves. For these reasons, coal-fired power plant will continue to be an important part of the power generation in the future. Also, since it emits more CO 2 per unit of electricity generated than other ways of generating energy such as nuclear and renewable energy, efforts are being made to reduce this amount. The USC (Ultra Super-Critical) boiler, which IHI has abundant design knowledge as well as proven construction and operation experiences, is contributing to CO 2 reduction. Since the USC boiler increases thermal efficiency of the power generation, overall CO 2 emissions is reduced. Also, the amount of fuel used per unit of electricity is decreased by adopting USC boiler, thereby reduces the fuel costs. USC boiler demand is increasing throughout the world from the perspective of CO 2 emissions as well as running costs. Also, the high operability of coal fired power plant is getting more important in recent years. In Europe, the percentage of renewable energy such as wind and solar power is increasing. However, the amount of electricity generated from them varies greatly by changes in the weather and time of day. Therefore, high operability that can absorb such variations is being important for coal-fired power plant. This paper introduces Trianel Kohlekraftwerk Lünen GmbH & Co. KG's Lünen Power Station in Germany, which is meeting the market demands such as high efficiency and high operability. 3

4 2. Project Outline The Lünen Power Station in Germany is a coal-fired power plant with a gross output of 813 MW. In July 2013 it was handed over to its owner, Trianel Kohlekraftwerk Lünen GmbH & Co. KG. See Figure 1 for a panorama of the plant. Fig.1 Trianel Lünen Power Plant For this project, IHI formed a consortium with Siemens AG (Figure 2). As EPC (engineering, procurement, and construction) contractor for the boiler and BOP (balance of plant), IHI carried out the basic and detailed design, production, machinery procurement, on-site installation and commissioning for the boiler and air quality control system (AQCS). This was IHI's first EPC project in Europe. Trianel Kohlekraftwerk Lünen GmbH & CO. KG TSPPC:Trianel Steam Power Plant Consortium (EPC Consortium Leader) Steam Turbine, Generator, Electrical Facility, Cooling Tower, etc. (Boiler EPC) Boiler, Pulverizer, Burner Ash Handling System AQCS, etc. Fig.2 Project structure 4

5 3. Design Overview and Characteristics 3.1 Specifications Figure 3 shows the general arrangement of the boiler, and Table 1 shows the boiler specifications. This USC boiler has main steam temperature of 600 C, reheat steam temperature of 610 C, and main steam pressure of 28.7 MPa. A tower type boiler, which is common in Europe, was introduced. The tower design occupies a small amount of area and therefore is suited for narrow plots. In Japan, IHI has supplied tower boilers to Electric Power Development Co., Ltd.'s New No. 1 and New No. 2 Isogo Thermal Power Plant. Table 1 Boiler specifications Item Coal Specification Boiler Type Ultra-Super Critical One-Through, Variable Pressure Operation, Reheat Type Steam Flow SH Outlet t/h 2,225 RH Outlet t/h 1,793 SH Outlet C 600 Steam Temp. BMCR RH Outlet C 610 Steam Press. SH Outlet MPa 28.7 RH Outlet MPa 6.2 Feed Water Temp. ECO inlet C 309 Design Ambient Temperature C 9 Firing Type Opposite Firing Draft Type Balanced Draft Minimum Operating Load (Coal Firing) % 25 Load Change Rate % min :Primary Air Fan (PAF) 2:Forced Draft Fan (FDF) 3:Gas Air Heater (GAH) 4:Steam Air Heater (SAH) 5:Burner 6:Over Air Port (OAP) 7:Side Air Port (SAP) 8:Primary Economizer 9:Secondary Economizer 10:Primary Superheater 11:Secondary Superheater 12:Tertiary Superheater 13:Final Superheater 14:Primary Reheater 15:Secondary Reheater 16:Separator and Separator Drain Tank 17:Bottom Ash Handling System 18:SCR Reactor Fig.3 General arrangement of the boiler 5

6 The main specifications of the boiler and air quality control system are shown in Table 2, and the system flow diagram is shown in Figure 4. Pulverizer and pulverized coal burner are made by IHI. So that the boiler would have high operability, Wide Range Burner, which has unique concept jointly developed by Shikoku Electric Power CO., Inc. Central Research Institute of Electric Power Industry and IHI, was adopted. The structure of Wide Range Burner is shown in Figure 5. The burner has a ring in the outer sleeve for adjusting the concentration distribution of pulverized coal. This makes stable combustion possible even in the low-load operation, because the concentration of pulverized coal is low in burner section. The operability improvements achieved by using the burner are discussed in Section 3.4. Table 2 General specifications of major equipment System Type Supplier Qty. Pulverizer IHI-VS 25S IHI 4 Burner Wide Range Burner IHI 32 Forced Draft Fan Axial Type TLT Turbo 1 Primary Air Fan Centrifugal Type TLT Turbo 1 Induced Draft Fan Axial Type TLT Turbo 1 Gas Air Heater Ljungstrom Type Balcke Dürr 1 De-Nitrification System Selective Catalytic Reduction System IHI 1 De-Sulfurization System Limestone-Gypsum System Andritz 1 Dust Collector Electrostatic Precipitator Balcke Dürr 1 Bottom Ash Handling System Dry Conveyor Clyde Bergemann 1 Fly Ash Handling System Pressure Transfer Claudius Peters 1 Boiler ESP IDF FGD SCR Reactor GAH SAH Fly Ash Handling System Stack/Cooling Tower FDF PAF Bottom Ash Handling System Pulverizer Fig.4 System flow diagram of the boiler and air quality control system 6

7 Burner Outer Sleeve Burner Throat Density Control Ring Burner Inner Sleeve Secondary Air Outer Vane Inner Vane Fig.5 Structure of a Wide Range Burner The air-gas system is comprised of singular system structure: it has one primary air fan (PAF), forced draft fan (FDF), induced draft fan (IDF), gas air heater (GAH), and air quality control system. Since it was the first experience for IHI to adopt singular systems to 800 MW-class power plants, when designing each equipment, IHI fully investigated whether or not problems would arise due to increase in machinery size, and readjusted their specifications, as necessary. For example, there was concern that leak rate of GAH would increase. In order to reduce this leak rate, instead of the tri-sector design which is often adopted for large coal fired power plants, a quad-sector design was introduced. In a quad-sector design, the primary air chamber is sandwiched between two secondary air chambers (Figure 6). It reduces the amount of direct leakage from the primary air chamber to the flue gas chamber, thereby the total leak rate can be reduced. Direction of Rotation Secondary Air Flue Gas Primary Air Secondary Air Fig.6 Plan view of the quart sector type GAH 7

8 3.2 Coal Properties 14 types of bituminous coal imported from South Africa, Russia, and so on were used for designing equipment. The properties of reference coal are shown in Table 3. When designing each equipment, characteristics of each type of coal were fully taken into account so that the boiler can operate in stable with all of them. Table 3 Properties of the reference coal Coal Reference Coal Item Heating Value (As Received) LHV MJ/kg Proximate Analysis (As Received) Ultimate Analysis (Dry Ash Free) Moisture % 7.5 Ash % 12.6 Volatile Matter % 24.8 Fixed Carbon % 55.0 Total Sulphur % 0.5 Carbon % 84.2 Hydrogen % 4.80 Nitrogen % 1.9 Oxygen % 8.4 Ash Fusion Temp. (Reducing) IDT C 1250 HGI High Efficiency As stated above, thermal efficiency of the plant is improved by adopting the boiler with USC steam condition. In addition to that, a parallel pass design for reheat steam temperature control was adapted to get more improvement of thermal efficiency. In the parallel pass design, gas pass of the upper part of the furnace (the boiler's head recovery area) was divided into a reheater side and a superheater side, and a damper was installed at the exit of each gas pass to adjust the amount of gas for controlling the reheat steam temperature. A water spray and/or a gas re-circulation system which cause loss of thermal efficiency are not necessary. 8

9 3.4 High Operability By using Wide Range Burner (described in Section 3.1), an expansion in the operating range with the same number of pulverizers and a reduction in the minimum load for coal combustion (25% load, 194 MW) was achieved (Figure 7). Number of Operating Pulveriyer: 4 Standard Burner 3 2 Wide Range Burner Lower Minimum Load Wider Operating Range Boiler Load (%) Fig.7 Operating range when using a Wide Range Burner It makes possible wide-range load change without having to start and stop the pulverizers, and therefore smooth load changing that matches electricity demand. Furthermore, by lowering the minimum load for coal combustion, it becomes possible to continuously operate the power plant when electrical demand is low in cases such as when the electricity generated by renewable energy is high. Thus, the heat loss that arises when starting and stopping the power plant can be reduced, and expensive start-up fuel oil can be conserved. When reducing the load for coal combustion, SCR (Selective Catalytic Reduction) catalyst inlet gas temperature was also taken into account. Since it is difficult to maintain temperature at the value which keeps the performance of De-Nitrification during low loads, an economizer bypass system was introduced. Some of gas is bypassed economizers, and this high temperature gas is mixed at SCR inlet, so that maintaining the gas temperature to required level. 9

10 3.5 Ensuring the Reliability of USC Conditions In order to ensure the reliability of the USC steam conditions boiler, IHI first exhaustively checked its compliance with EN code, and chose field-proven materials which IHI has many experiences and knowledge. In the superheater and reheater, SUPER304H was used for heated parts and 9Cr was used for the non-heated parts. Furthermore, two headers and four pipes arrangement were adopted as show in Figure 8, to comply with the EN standard restrictions on upper limitation of pipe wall thickness. Furthermore, the pipes of each superheater outlet was crossed from left to right and center to edge respectively, thereby minimizing the steam temperature imbalance. HP Turbine Pri. SH Sec. SH Ter. SH Fin. SH Fig.8 Arrangement of super-heater tubers 13CrMo4-5 (equivalent to ASME SA213T12) which is field-proven material was used for furnace wall tubes. In European market, 7CrMoVTiB10-10 (equivalent to ASME SA213T24), which has higher temperature strength than 13CrMo4-5, has been generally used for the furnace wall tubes of tower type boilers. However, 7CrMoVTiB10-10 is known for being difficult to fabricate as a panel. Therefore, IHI had carried out a mock-up test to fabricate furnace wall panels with of 7CrMoVTiB From the result, IHI refrained from using it because the reliability of the fabrication cannot be ensured, and decided to adopt field-proven 13CrMo4-5. Radiation superheaters were placed in the upper part of the furnace to keep the furnace outlet steam temperature within an appropriate range for 13CrMo

11 3.6 Complying with European Laws, Regulations, Standards, and Safety Demands Products sold in the European Union are obligated to have the CE marking on them. To be complied with PED (Pressure Equipment Directive), the boiler is designed and fabricated in compliance with harmonized standards of EN code. Furthermore, all equipment and material were carefully verified and controlled in accordance with REACH (Registration, Evaluation, Authorization and Restriction of Chemicals). Also, in response to the customer's request, a hazard and risk analysis based on IEC was carried out. For processes which has possibility to inflect physical harm to operators, instruments and control systems were made to meet IEC 61511's Safety Integrity Level (SIL), thereby creating a highly trustworthy system. 4. Commissioning Results 4.1 Performance Test Results Table 4 shows the results of the performance test. It was confirmed that the net electricity output and the net plant efficiency were both met the design values. The net plant efficiency was approximately 46% that is a world top-class rate for coal-fired power plants. Similarly, it was confirmed that all flue gas emission such as NO X and SO X met the design values. Table 4 Properties test results Item Design Value Performance Test Result Boiler Load % Net Output MW Net Plant Efficiency (LHV Base) NOx at Stack Inlet SOx at Stack Inlet CO at Stack Inlet Dust at Stack Inlet % mg/nm³ (Dry, 6%O₂) mg/nm³ (Dry, Actual O₂) mg/nm³ (Dry, Actual O₂) mg/nm³ (Dry, Actual O₂)

12 4.2 Checking Operability The operating condition at 25% coal combustion load is shown in Figure 9. It can be seen that main steam temperature and pressure stayed almost flat, and the operation condition at 25% load was stable. The stable combustion condition in the furnace was observed at the load, and it was demonstrated that the boiler can operate continuously at 25% load. Coal Flow (kg/s) Boiler Load (%), Main Steam Pressure (MPa) Gross Electric Output (MW) : Boiler Load : Coal Flow : Gross Electric Output : Main Steam Pressure : Main Steam Temperature : Hot Reheat Steam Temperature :30 12:00 12:30 13:00 13:30 Time ( h : min ) Main Steam Temperature, Hot Reheat Steam Temperature ( C) Fig.9 Minimum load operation with pure-coal firing The results of the 60%-90% load change test are shown in Figure 10. The operating conditions during and after the load changes were stable, and the design load change rate of 4% min -1 was achieved. By widening the operating ranges of the pulverizers, a smooth load change that follows demand without the starting and stopping of pulverizers was realized : Boiler Load : Gross Electric Output Demand : Main Steam Temperature : Coal Flow : Gross Electric Output : Hot Reheat Steam Temperature Boiler Load (%) Gross Electric Output Demand Gross Electric Output (MW) Coal Flow (kg/s) :00 10:00 11:00 12:00 13:00 14:00 15:00 Time (h : min) Fig.10 Load swing test result Main Steam Temperature, Hot Reheat Steam Temperature ( C) 12

13 5. Conclusion This paper presented an overview of the Lünen Power Station project, its design, and its characteristics. Furthermore, based on commissioning results, it was shown that this power station meets the market demands of high efficiency and operability. It can be expected that demand for highly efficient and operable coal-fired power generation will increase further in the future. IHI will continue to provide coal-fired power plants which meet the demands and have higher quality, with taking the experience on Lünen Power Station. 13