(70) Therefore, the risk of sulphuric acid dew point attack ... - DTI Home

More documents

Recommendations

Info

conditions of some established and more recently developed gas turbines are shown in Table 5 below: Gas Turbine Turbine inlet temperature (°C) Siemens/Westinghouse 501G (a 60Hz machine) (87) Turbine exhaust temperature (°C) Mass flow (kg/s) 1427 600 535 GE 9351FA 1327 606 636 Alstom GT 26 1260 641 549 GE 9001H 1427 621 685 Table 5: Turbine inlet/exhaust gas temperatures and mass flow rates on some modern gas turbines [65] . The Alstom GT 26 (and GT 24) gas turbine uses sequential combustion in two annular combustion chambers to achieve improved efficiency. This is different to the conventional approach to gas turbine combustion, which is carried out in a single stage and requires increasingly high firing temperatures and complicated cooling technologies [66] . The exhaust temperature is the highest of any commercially available gas turbine. The GE 9001H is designed to give a combined cycle thermal efficiency of 60% and the first of its kind is being installed at Baglan Energy Park in South Wales. The efficiency improvement is due to the high firing temperature, which is made possible by the use of large single crystal airfoils, superior component and coating materials and a closed-loop steam cooling system (see Section 4.3.1) [67] . The implications of this type of cooling system for HRSG water/steam chemistry are not trivial and are discussed in Section 3.5.9. In general, the latest generation of gas turbines, with their increased gas turbine outlet conditions are not anticipated to be a major concern as far as the HRSG pressure parts are concerned, as materials issues at these temperatures have been successfully tackled on conventional coal-fired plant. For these increased temperatures, GT diffuser ducts, HRSG inlet ducts and casings are likely to be internally insulated in the higher temperature regions. Currently used internal insulation liner materials can cope with these relatively small increases in temperature (internal insulation has been proven on CHP plant with supplementary firing up to around 850°C). The most likely area to be impacted is that of non-cooled support components, particularly on vertical gas-flow HRSGs e.g. HP superheater/reheater tube sheets and support links. This may require more extensive use of higher grade alloys such as modified 9% chrome (P91) or stainless steel for support components. There may even be a need to employ water/steam cooled support tubes for high temperature tube banks on vertical gas-flow HRSGs (akin to the rear pass of a conventional coal fired boiler). This method of support has largely been limited to supplementary fired vertical gas flow HRSGs in the past.
4.3.6 Supercritical Technology Currently state-of-the-art supercritical pulverised fuel fired steam power generation plants exist and operate at up to nominally 300 bar and 600°C steam output with net efficiencies of ~45% LHV [68] . Due to advances in materials technologies steam temperatures and cycle efficiencies have gradually improved and are set to continue to do so. Targets of final steam conditions of 650-700°C have been set for 2020 and associated cycle efficiencies of around 50-55% are expected. The recognised advantages of adopting a supercritical steam cycle in addition to the obvious improvements to cycle efficiency are [68] :- • CO2 emissions are reduced by about 15% per unit of electricity generated when compared with typical existing sub-critical plant. • Exceptionally good part load efficiencies are achievable, typical half the decrease in efficiency exhibited by sub-critical plant. • Plant costs are considered comparable with sub-critical technology. Much of the technology surrounding supercritical technologies is not new and a great deal of development work was done in the 1950s and 1960s. At this time countries such as the UK kept a predominantly sub-critical power base due to the unreliability, expense and poor operational flexibility of these early designs. However, elsewhere in Europe and in Japan, development and refinement continued to the extent that supercritical steam is now considered one of the leading clean coal technologies. Currently 10% of orders for new coal fired power generation plant are for supercritical steam cycles and whilst future orders are difficult to predict, estimates suggest a steady rise in the adoption of this technology [68] . Supercritical steam cycles are not limited to coal fired plants exclusively. In theory, supercritical steam cycles can be used for any technology incorporating a steam cycle to generate electricity. Therefore the benefits are considered applicable to HRSGs within combined cycle gas turbine systems. With advances in gas turbine technology, combined cycle units are now larger and HRSGs are operating at higher temperatures. Previously both these factors were lacking and thus directly affected the commercial and technical viability of the supercritical HRSG. 4.4 New Applications for HRSGs 4.4.1 The Role of HRSGs in IGCC Plant 4.4.1.1 IGCC Plant Description Whilst gas turbine technology has been applied previously in natural gas and oil fired combined cycle plants, the development of the Integrated Gasification Combined Cycle (IGCC) allows both solid and liquid fuels to be the main (88)
Page 1 and 2: Therefore, the risk of sulphuric ac
Page 3 and 4: components in terms of thermal fati
Page 5 and 6: 3.8.2 Operating Costs Fixed operati
Page 7 and 8: and bio-gas from anaerobic digestio
Page 9 and 10: 4 NEW AND DEVELOPING TECHNOLOGIES 4
Page 11 and 12: many existing combined cycle gas tu
Page 13 and 14: 4.3 Improvements to Cycle and Other
Page 15 and 16: The world’s first operational ste
Page 17: application for which OTSGs may be
Page 21 and 22: Initially, the coal is pulverised i
Page 23 and 24: Figure 33: Diagram of a typical IGC
Page 25 and 26: Plant Country Start Fuel Process MW
Page 27 and 28: • The use of HRSGs within IGCC pl
Page 29 and 30: Company Alstom Aprovis Erie Innovat
Page 31 and 32: considered the top ranking is alter
Page 33 and 34: Figure 34: Average percentage of bu
Page 35 and 36: European (CEE) countries. The marke
Page 37 and 38: 6.4.1.2 Fluctuations in the Price o
Page 39 and 40: consents policy had the effect of c
Page 41 and 42: equipment, increasing the opportuni
Page 43 and 44: 6.5.1 Possible Non-Technical Barrie
Page 45 and 46: Detailed studies of CCTs within the
Page 47 and 48: knowledge, expertise and experience
Page 49 and 50: Up until the mid 1990’s and opera
Page 51 and 52: Company Ultimate Parent Company BIB

(70) Therefore, the risk of sulphuric acid dew point attack ... - DTI Home

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?