04/11/2023

DLN 1.0 (Dry Low NOx System)

Prepared by: Ejaz Ali Soomro

04/11/2023

Introduction

DLN Stands for Dry Low NOx System

Used to improve the combustion system

Reduce emissions level

NOx level 15-9ppm

04/11/2023

04/11/2023

DLN 1.0 Combustion System

DLN 1.0 is a two stage premixed burner.

04/11/2023

The Gas Turbines Control System “Speedtronic” controls the fuel and associated system Dry Low NOx (DLN) is a two-stage premixed combustor designed for operation on natural gas. The combustor operates by premixing the gas fuel with the air in the first stage, and then combusting the mixture in the second stage. The fuel/air mixture flame has more mass than a standard diffusion fuel flame, and so burns colder with less NOx produced. The DLN combustor also operates on #2 distillate liquid fuel, but not with premixing the fuel with air.

DLN 1.0 Combustion System

04/11/2023

While operating on liquid fuel, water injection is used for NOx control. DLN operates at a constant flame temperature, and so has limited turndown in the premix operation mode. A product called “inlet bleed heat” mixes compressor discharge air with inlet air to extend turndown with DLN premix combustion. The DLN combustor has six individual fuel nozzles in the primary combustion zone and a single fuel nozzle in the secondary combustion zone. The DLN combustion system offers lower NOx emissions levels on gas fuel fired units without the parts life reduction associated with water or steam injection NOx reduction systems.

DLN 1.0 Combustion System

04/11/2023

DLN 1.0 modes

Primary – Fuel to the primary nozzles only. Flame is in the primary stage only. This mode of operation is used to ignite, accelerate and operate the machine over low- to mid-loads, up to a pre-selected combustion reference temperature. The typical firing temperature TTRF range for this mode is from startup ignition through full speed no load to approximately 1500°F.Lean-Lean – Fuel to both the primary and secondary nozzles. Flame is in both the primary and secondary stages. This mode of operation is used for intermediate loads between two pre-selected combustion reference temperatures. Typical firing temperaturesfor the Lean-Lean mode are between 1500°F and 1950°F

04/11/2023

DLN 1.0 modes

Secondary – Fuel to the secondary nozzle only. Flame is in the secondary zone only. This mode is a transition state between lean-lean and premix modes. This mode is necessary to extinguish the flame in the primary zone, before fuel is reintroduced into what becomes the primary premixing zone. A typical firing temperature for this mode is 1900°F.Premix – Fuel to both primary and secondary nozzles. Flame is in the secondary stage only. This mode of operation is achieved at and near the combustion reference temperature design point. Optimum emissions are generated in premix mode. The typical firing temperature range for this mode of operation is above 1900°F.

04/11/2023

TTRF (Turbine Combustion Reference Temperature)

The control variable TTRF1 (Combustion Reference Temperature) signifies mode transfer points and fuel split schedules for the DLN system.

Appropriate values of TTRF1 are then stored in the controller as combustion mode transfers points so that the combustor may operate properly over its range.

TTRF1 is also used to modulate the fuel system splits over the load range. It is not used to regulate the load level of the machine.

TTRF1 is calculated from measurements of barometric pressure, compressor discharge pressure and temperature, and turbine exhausts temperature obtain from the standard turbine instrumentation.

04/11/2023

TTRF (Turbine Combustion Reference Temperature)

To ensure acceptable part load turndown behavior, the database covers a span of ambient temperatures, and full range modulation of Inlet Guide Vane and Inlet Bleed Heat. It is targeted to provide a consistent reference for combustor operating behavior.

04/11/2023

DLN 1.0 Inlet Guide Vane OperationThe load range associated with DLN modes varies with the degree of inlet guide vane modulation and, to a smaller extent, with the ambient temperature. At ISO ambient, the premix operating range is 50% to 100% load with IGV modulation down to 42°, and 75% to 100% load with IGV modulation down to 57°. The 42° IGV minimum requires an inlet bleed heat system.If required, both the primary and secondary fuel nozzles can be dual-fuel nozzles, thus allowing automatic transfer from gas to oil throughout the load range. When burning natural gas or distillate oil, the system can operate to full load in the lean-lean mode . This allows wet abatement of NOx on oil fuel and power augmentation with water on gas.

04/11/2023

Spark plugs arrangement for DLN 1.0 Combustor

The spark plug and flame detector arrangements in a DLN-1 combustor are different from those used in a conventional combustor. Since the first stage must be re-ignited at high load in order to transfer from the premixed mode back to lean-lean operation, the spark plugs do not retract. One plug is mounted near a primary zone cup in each of two combustors.

04/11/2023

Flame detectors arrangement for DLN 1.0 Combustor

The system uses flame detectors to view the primary stage of selected chambers (similar to conventional systems), and secondary flame detectors that look through the center body and into the second stage.The primary fuel injection system is used during ignition and part load operation. The system also injects most of the fuel during premixed operation and must be capable of stabilizing the flame.

04/11/2023

04/11/2023

DLN 1.0 liquid fuel operation is limited to the Primary and Lean-Lean modes of combustion. The unit will startup and load up from full speed no load in Primary mode. A transition to the Lean-Lean mode will be made at an approximate firing temperature of 1600°F by diverting a portion of the liquid fuel to the Secondary combustion zone. Liquid fuel operation will occur in the Lean-Lean mode with approximately a 50/50 primary to secondary fuel split distribution above TTRF= 1600°F until Base Load.

DLN 1.0 Liquid Fuel Operation

04/11/2023

The following display messages will appear on the SPEEDTRONIC control panel CRT in orderto inform the operator of the current combustion mode of operation:1. Primary Mode2. Lean-Lean Mode Pos3. Lean-Lean Mode Neg4. Lean-Lean Ext. Mode5. Secondary Transfer6. Secondary Load Recovery7. Premix Transfer8. Premix Steady State

DLN 1.0 Display Messages

04/11/2023

Operation of the gas turbine with reduced minimum IGV settings (typically less than 57 Deg) can be used to extend the Premix operating region to lower loads. Reducing the minimum IGV angle allows the combustor to operate at near a constant firing temperature high enough to support Premix operation while maintaining a sufficient fuel to air ratio.Inlet heating through the use of recirculated compressor discharge airflow is necessary when operating with reduced IGV angles in order to protect the turbine compressor.

DLN Inlet bleed Heating

04/11/2023

Inlet heating protects the turbine compressor from stall by relieving the discharge pressure and by increasing the inlet air stream temperature. Also, inlet heating prevents ice formation due to increased drop across the reduced angle IGVs.The DLN Inlet heating system regulates compressor discharge bleed flow through a control valve and into a manifold located in the compressor inlet air stream. The control valve varies the inlet heating air flow as a function of the IGV angle.

DLN Inlet bleed Heating

04/11/2023

At minimum IGV angles the inlet bleed flow is controlled to a maximum of 5% of the total compressor discharge flow. As the IGVs are opened at higher loads, the inlet bleed flow is turned down linearly until shutoff.The inlet bleed heat control valve is monitored for its ability to track the command set point. If the valve command set point differs from the actual valve position by a prescribed amount for a period of time, an alarm will annunciate to warn the operator.

DLN Inlet bleed Heating

04/11/2023

If the condition persists for an extended amount of time, the inlet bleed heat system will be tripped and the IGVs will be reset to their normal schedule.The inlet bleed heat system also looks to detect a temperature rise in the compressor inlet airflow as an indication of flow when the control valve is opened. Failure to detect a sufficient temperature rise in a set amount of time will cause the inlet bleed heat system to be tripped and an alarm annunciated to alert the operator.

DLN Inlet bleed Heating