1.4.0 DLN-2.6 + Combustion System

4.0 DLN-2.6 + Combustion System

The combustion system is a reverse-flow design with 16 combustion chambers arranged around the periphery of the compressor discharge casing. Combustion chambers are numbered counter-clockwise starting with the chamber just left of the chamber at top dead center when looking aft end. This system also includes the fuel nozzles, a spark plug ignition system, flame detectors, and crossfire tubes.

High pressure air from the compressor discharge is directed around the aft end of the transition piece. Most of the compressor discharge air enters the holes in the aft end of the transition piece to cool the transition piece and for annulus between the flow sleeve and liner, through holes in the aft end of the flow sleeve. This air passes through the quaternary fuel ring and then enters the combustion zone through the cap assembly for proper fuel combustion. Fuel is supplied to each combustion chamber through six nozzles designed to disperse and mix the fuel with the proper amount of combustion air (and to the quaternary ring at during baseload operation). Hot gases, generated from burning fuel in the combustion chambers, flow through the impingement cooled flow sleeve and transition piece to the turbine.

4.1 Combustor Configurations for Fuel Type:

Dual Fuel
This configuration is capable of operation on either natural gas or liquid fuel. The fuel type can be changed gas to liquid to gas while the GT is operating.

Gas Fuel Only
The fuel nozzles feed only natural gas to the combustion system, with no provision for liquid fuel operation.

Liquid fuel only
The fuel nozzles feed only liquid fuel and water into the combustion system, with no provision for gas fuel.

·         On gas fuel, the combustor operates on 6 fuel nozzles per combustor, where the number of fuel nozzles fueled increases as the GT load increases. One nozzle is fueled from FSNL to low load; three nozzles are fueled from low load to intermediate load; and six nozzles are fueled plus the quaternary fuel circuit from intermediate load to baseload. Emissions complaint operation required all fuel circuit to be fueled and GT firing temperature to be above a threshold temperature.

·         On oil operation, this combustor operated in diffusion amide across the entire load range, with only the outer 5 fuel nozzles fueled. Water injection is also injected by the fuel nozzles into the combustor for NOx reduction.

4.3 Outer Combustion chambers and Flow Sleeves

The outer combustion chamber, or casing, acts as the pressure vessel for the combustor. They also provide flanges for the fuel nozzle-end cover assemblies, crossfire tube flanges, spark plugs, flame detectors and false start drains. The flow sleeve forms an annular space around the cap and transition piece assemblies that directs the combustion and cooling into the forward end of the combustor fuel nozzle jet.

4.4 Cap, Flow Sleeve, and Transition Piece Assemblies

The combustion flow sleeves and transition pieces are passively cooled on their outside with air directed by the impingement sleeve to the forward end of the combustor and fuel nozzle inlet. Ridges on the liner outer surface augment the cooling effectiveness. The inner surfaces of the transition piece and flow sleeve have thermal barrier coating to reduce metal temperatures and thermal gradients. The aft end of the transition piece transforms the combustor annular flow into  flow profile to be fed into the Stage 1 Turbine Nozzle. The Cap has six burner tubes that engages each of the six fuel nozzles. The cap is cooled by effusion cooling passages.

4.5 Fuel Nozzle End Covers

There are six fuel nozzles assemblies in each combustor. They arranged with 1 located in the center and five arranged around the outer edge. Each fuel nozzle premixes the inlet air and gas fuel, and then forwards this mixture to the combustor reaction zone for burning. The outer fuel nozzles contain a liquid fuel and water passage down the center of the fuel nozzle for operation on oil, where oil and water is injected directly into the combustor. Water is injected into the reaction zone when the combustor is to be operated within emissions compliance on oil fuel.

4.6 Quaternary Fuel Ring

Each combustion chamber contain a Quaternary fuel ring located between the combustion casing and the CDC. Fuel is instructed at intermediate load and above.

4.7 Crossfire Tubes

All combustion chambers are interconnected by crossfire tubes to provide means for ignition of the chambers without ignitors. The outer chambers are connected with an outer crossfire tube and the combustion liners are connected by the inner crossfire tubes.

4.8 Spark Plugs

The combustor is ignited with two spark plugs that are positioned within the combustor downstream of a fuel nozzle. Once the combustor is ignited, the pressure from the combustor forces the ignitor tip to retract from the combustor for continous operation. These spark plugs receive their energy from high energy-capacitor discharge power supplies. Once the combustor chamber is ignited with the spark plug, the remaining chambers are ignited by the flame passing through the crossfire tubes that interconnect the reaction zone of the remaining chambers.

4.3 Flame Detectors

A flame monitoring system is used consisting of 4 flame detectors. The signals from the flame detectors are sent to the control system which uses an internal logic system to confirm whether the combustors are ignited or extinguished.