ANALYSIS OFVIBRATORY STRESS OF INTEGRAL SHROUD BLADE FOR MECHANICAL DRIVE STEAMTURBINE by Yasutomo Kaneko
The advanced integral shroud blade (ISB) structure has been developed to improve the reliability and thermal efficiency of mechanical drive steam turbines. This advanced ISB has been applied to not only the control stage blades but also the intermediate stage blades. Turbines using these advanced blades have been successfully operated. This paper presents the analysis method to calculate the vibratory stresses of the ISB caused by the stage interaction force and the shock load. The vibration response characteristics are explained and comparisons are made to the advanced ISB structure and the conventional grouped blade structure, using the calculated results. Additional verification test results to confirm the validity of the proposed analysis method are also shown.
New Technologies Of Synthesis Gas Compressor Drive Steam Turbines For Increasing Efficiency And Reliability.
Recently, synthesis gas compressor drive steam turbines have required upgrading to increase efficiency and reliability for saving both operation and maintenance costs in many ammonia plants. This paper introduces the latest practical technologies to achieve very high performance. Examples include a highly unique assembly of integral shrouded blades, a new profile design procedure for both fluid loss reduction and increased strength against high-speed and high-stage power. Finite-element and computational fluid dynamics analysis results of new blades and nozzles are discussed while comparing experimental data from a cascade test and a rotating blades shaker test. These results are shown in terms of actual loss distribution, efficiency measurement, and vibration/stress mode on rotating blades including design criteria. Other useful applications of new technologies to reduce steam leakage and increase last stage blade performance are introduced. These involve modification of the exhaust casing and a new turning device. In particular, high speed and high loading are inevitable in synthesis gas compressor drive steam turbines. In order to improve operation reliability considering these factors, a special cooling design is applied for the thrust bearings to reduce the pad metal temperature. The results of this analysis and basic experimental data are discussed in detail. Furthermore, examples of actual job applications are explained, and high-speed balancing, mechanical running test, and site performance test results are shown. INTRODUCTION Synthesis gas compressor drive steam turbines are the most important rotating equipment in the field of methanol and ammonia plants. They are specially designed to cope with high speeds (exceeding 10,000 rpm) and high output powers (up to 40,000 kW) and have been applied as both end drive machines for high-pressure (HP) and low-pressure (LP) compressors. In the process of these plants, efficiency improvement is achieved through such means as a chemical catalyst, and as a result the required maximum power tends to decrease to less than 30,000 kW. Thus the efficiency of these turbines is focused on the design of the plant in order to minimize the margin on heat and flow balance for the most cost effective solution. In contrast, large capacity plants for methanol or new fuel are under consideration in a case study. For these mega plants, the synthesis gas compressor drive steam turbines with large output powers (exceeding 50,000 kW) will be required and realized in the near future. In this sense, these synthesis gas compressor drive steam turbines have to be continuously improved and upgraded to increase their efficiency and reliability for saving both operation and maintenance costs. As a starting point to this improvement, the performance of several existing extraction-condensing turbines actually in operation undergoes detailed analysis of their high-pressure and 75 NEW TECHNOLOGIES OF SYNTHESIS GAS COMPRESSOR DRIVE STEAM TURBINES FOR INCREASING EFFICIENCY AND RELIABILITY by Tomoyoshi Sasaki Manager, Turbine Design Section Satoshi Hata Manager, Turbine Design Section and Kyoichi Ikeno Mechanical Engineer, Turbine Design Section Mitsubishi Heavy Industries, Ltd. Hiroshima, Japan low-pressure sections. According to the analysis results, practical countermeasures are considered including the application of newly developed nozzles and integral shrouded blades (ISB) for speed control stage having mostly high-stage power. In this paper, the process of key components development is introduced by showing the results of finite-element analysis (FEA), computational fluid dynamics (CFD) analysis, lab evaluation tests, actual application, and performance evaluation based on onsite data. STRATEGY OF MODIFICATION The cross section of synthesis in a gas compressor drive steam turbine and the key features for improvement are shown in Figure 1 to make the concept of modification clear. The smooth flowpath from the inlet governing valve diffusers through HP and LP sections to the exhaust casing is designed by CFD in order to minimize losses. The first stage generates a maximum 12,000 kW and accounts for the greater part of the total output power. For this stage, the combination of nozzle and ISB with developed profiles is applied to increase stage efficiency dramatically, as explained later in this paper. The ISB with advanced profile is used for all other stages. In particular, the last stage has a bow nozzle to decrease secondary flow losses. In addition, a slant labyrinth seal is applied in the high-pressure side and extraction portion. This special seal can decrease the leakage by about 30 percent. The journal and thrust bearings have large thrust forces, high-pressure intensity, and heat load due to high-speed friction losses. For the purpose of decreasing metal temperature, back metal cooling for pads and copper back pads are applied. The latest material coating technology is used for improving reliability for long-term operation. A special coating is applied to the first stage nozzles and LP section blading to prevent solid and drain erosion. Figure 1. Strategy of Modification. DEPTH ANALYSIS OF PERFORMANCE A synthesis gas compressor drive steam turbine in actual operation at site was chosen for a case study, and a detailed performance analysis was carried out to make a loss map, considering the HP and LP sections separately. Loss of Flowpath Through Nozzle and Blade The calculated loss distribution for each stage is shown in Figure 2. From these analysis results, in the case of conventional nozzle and blade, the first stage of speed control stage accounts for a large part of the total loss, which consists of leaving loss, tip leakage loss, nozzle, and blade loss related to their profiles. The third stage of extraction pressure control stage loss is smaller than the first stage, but stage loss distribution ratio is almost the same—and these kinds of losses have to be minimized. For efficiency improvement, these control stages will be highlighted and the matching of nozzle and blade will have to be improved to prevent flow separation, flow velocity deceleration, and tip leakage. This will be achieved by profile modification and reaction control as shown in Figure 3. For decreasing losses effectively, the secondary flow loss of the nozzle and blade is considered as shown in Figure 4. The conventional blades shrouded by tenons have very high centrifugal forces for high-speed synthesis gas compressor steam turbines, and the nozzles are designed to have large gauging in order to minimize the blades height. For these large gauging nozzles, the profile cannot be optimized, and the nozzle exit velocity angle into the blade is so large that the stage overall efficiency tends to decrease. In the case of large stage power and large steam flow, this height restriction becomes critical, and to increase the blade strength, the application of ISB is one of the most important countermeasures. Figure 2. Actual Loss Analysis. Figure 3. Conventional Nozzle and Blade. Casing Internal Leakage Except for nozzle and blade losses, internal leakage through the split surface of diaphragms inside the casing will be considered in order to evaluate the turbine performance practically. The expected leakage ratio for each stage and related portion is described in Figure 5. According to leakage flow rate and energy level, the leakage from the HP section and extraction portion apparently affects the overall turbine efficiency. Based on the results of the above loss and performance analysis, reaching the target of performance improvement is addressed as shown in Figure 6. PROCEEDINGS OF THE THIRTY-FIRST TURBOMACHINERY SYMPOSIUM • 2002 76 NEW SEAL HIGH EFFICIENCY NEW NOZZLE NEW BLADE BOW NOZZLES SMOOTH PATH CFD DESIGN SMOOTH PATH CFD DESIGN
Targeting oral anticoagulation
Clinical Pharmacology & Therapeutics (2000) 68, 4–5; doi: 10.1067/mcp.2000.108197