The steam generated from the SGT6-5000F with the boiler steam will provide a good match for the existing steam turbine.
A new economizer section is recommended to be added at the outlet of the boiler to add more economizing surface for optimum performance. The existing superheater, reheater and economizer sections inside the boiler will still be used with the new repowered system. The existing regenerative air heaters will be used to preheat the fresh combustion dilution air.
It should be noted that the existing burners will have to be modified to handle the lower O2 in the repowering combustion air to maintain flame stability.
Because the exhaust flow from the combustion turbine (after dilution) will match the boiler flue gas flow, boiler structural modifications are not required.
A new, single pressure HRSG will be added to operate with the SGT6-5000F(4) combustion turbine.
The new HRSG will consist of a superheater section, high pressure evaporator section and an economizer section.
Thermal analysis
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/>Several heat balances/cycle analyses were conducted to predict the performance of the proposed repowering project. GE’s GateCycle Software was used as the main heat balance software for this study. Different balances with different combinations of combustion turbines were developed and compared. Only the results of the most optimum case are presented in detail in this paper.
Heat balance The following tables (Tables 1, 2, 3) summarize the predicted performance of the proposed power plant with the selected combustion turbines.
Table 4 summarizes the results obtained from comparing other combinations of combustion turbine options to repower the boiler.
Capital cost estimate The capital cost estimate presented in this paper is based on an approximate ±25 percent accuracy range.
This estimate is based on vendor pricing for major equipment, such as the combustion turbines, HRSG and economizer received in the first quarter of 2008.
Assumptions In developing the estimate, it was assumed that the project will be performed using a general contractor familiar with this type of repowering retrofits. The contractor will be responsible for his own engineering, material procurement and construction. The estimate was based on a 50-hour work week.
Allowances Costs for erection supervision on-site to oversee the installation of specific equipment were included in the total equipment pricing. This includes the erection and start up supervision for the combustion turbines and HRSG.
Direct costs Equipment: This cost includes major equipment, such as the combustion turbines, HRSG, additional economizer surface, burner and windbox modifications; as well as balance of plant (BOP) equipment such as duct work, expansion joints, oil water separator, sump pumps, blowdown tanks and steam/water sampling. Prices for the main process systems and equipment were from budget proposals prepared from written specifications. Other equipment prices were based on budget quotations and current in-house price information.
Installation: Equipment installation cost includes erection labor, foundations, piling, paint, insulation and demolition or relocation.
Buildings: Building costs include an electrical room. Other structures, such as pipe bridges support steel, grating, stairs and handrails are included in this total cost as well.
Piping: This cost includes all process piping, heat tracing and insulation. Piping costs were based on vendor pricing for main steam and factored pricing for the balance of piping system.
Electrical: This cost includes substation transformers and switchgear, motor control centers, batteries and charger, power wiring, grounding and switchyard allowance. Electrical costs were based on vendor pricing and in-house information.
Instrumentation: This cost includes DCS equipment and configuration, control panels, field instruments, as well as supply and installation of tubing and wiring. Instrumentation costs were based on preliminary P&ID’s prepared for this study.
Site preparation and services: This cost includes all associated site work, including gates/fences, drainage, underground utilities, yard lighting, fire loop, roads and paving.
