The government of Thailand has asked industrial companies to reduce their emissions, in support of a national initiative to improve the country's air quality. Thaioil Power, a subsidiary of Thai Oil, which is Thailand's largest oil refiner, has taken some significant steps in that direction.
Thaioil Power recently invested in GE's advanced Dry Low NOx (DLN) technology to replace combustion systems on two GE Frame 6B gas turbines at a cogeneration plant in Sriracha in Chonburi Province. The 130-megawatt plant supplies power and steam for the Thaioil refinery at the site, with excess power sold to EGAT/Grid, the national power generation company. The refinery produces 275,000 barrels of oil per day, which represents more than a fifth of Thailand's total refining capacity.
As a result of the DLN technology upgrade, the Sriracha cogeneration plant now has the lowest level of NOx emissions for any power generation site in Thailand: 10 parts per million (ppm). This is a reduction from the previous levels of 42 ppm.
A reduction of 32 ppm NOx on this type of gas turbine means a reduction of 8.5 kg of NOx per hour, per turbine, equivalent to 67,500 kgs of NOx eliminated per year. The average passenger car emits 0.5 g/km while driving in Bangkok (EC Level 3 Emissions Standard). Assuming 20,000 km driven per car, per year, that totals 10 kg of NOx per car, per year. The bottom line: the emissions reduction per gas turbine at the Thaioil site is equivalent to taking 6,750 cars off the road in Bangkok.
The DLN technology upgrade also eliminated the need to use steam injection for NOx abatement, allowing the steam produced from the gas turbine exhaust to be used for other refinery processes.
The project supports Thaioil Power's overall environmental objectives, and is part of the company's Corporate Social Responsibility initiative. The technology upgrade and the subsequent improvement in emissions control qualified the Sriracha plant for tax incentives from Thailand's Board of Investment.
The completed DLN retrofit project, from order issue to engineering, procurement and installation, was completed in only three months, while the actual retrofits only took a few weeks per machine. This rapid pace met Thaioil Power's aggressive schedule and kept the project within the planned maintenance window.
Origin of DLN Technology
Over the past 20 years, manufacturers of gas turbine combustors have been striving to keep pace with a changing regulatory landscape. One of the prominent pollutants that needed to be dealt with was NOx. Early gas turbine combustors employed a diffusion flame that inherently had good stability but poor emissions characteristics. When emissions needed to be controlled, water or steam was used as a diluent and NOx was brought down to less than 50 ppm -- at the expense of reliability and performance.
About 15 years ago, gas turbine manufacturers were challenged to meet lower emissions requirements without diluents injection. DLN technology was GE's response to that challenge.
The DLN-1 combustor was GE's first commercially available premixed combustor. DLN1-style combustors have been used in a variety of E class combustors. Overall, DLN combustors have compiled more than 23 million hours of operation on more than 800 units worldwide.
The specific technology selected for the Thaioil Power project was GE's advanced DLN-1 combustion system, which has been designed to help gas turbine operators worldwide meet lower emissions requirements without diluents injection. This technology is introduced at the front end of the gas turbine fuel nozzle, to better mix the fuel with the air as it goes into the fuel nozzle. The technology also is implemented at the other end of the fuel nozzle to better manage how the fuel goes into the combustion. This helps to optimize the flame dynamics and reduce the temperature, thus reducing the emissions.
DLN Performance
GE DLN systems integrate a staged pre-mixed combustor, the gas turbine's Speedtronic™ controls and the fuel and associated systems. There are two principal measures of performance. The first is meeting the emissions levels required at base load on both gas and oil fuel and controlling the variation of these levels across a load range of the gas turbine.
The second measure is system operability, with emphasis placed on the smoothness and reliability of combustor mode changes, ability to load and unload the machine without restriction, capability to switch from one fuel to another and back again, and system response to rapid transients (generator breaker open events or rapid swings in load).
GE's design goal is to make the DLN system's operation transparent to the user; in other words, the gas turbine operator does not know whether a DLN or a conventional combustion system has been installed. A significant portion of the DLN design and development effort focused on system operability. As operational experience has increased over the years, design and development efforts have moved toward hardware durability and extending combustor inspection intervals.
Design of a successful DLN combustor for a heavy duty gas turbine also requires the designers to develop hardware features and operational methods that simultaneously allow the equivalence ration and residence time in the flame zone to be low enough to achieve low NOx but with acceptable levels of combustion noise (dynamics), stability at part-load operation and sufficient residence time for CO2 burnout.
The GE DLN-1 combustor is a two-stage premixed combustor designed for use with natural gas fuel and capable of operation on liquid fuel. The combustion system includes four major components: fuel injection system, liner, venturi and cap/centerbody assembly. These components form two stages in the combustor. In the premixed mode, the first stage thoroughly mixes the fuel and the air and delivers a uniform, lean, unburned fuel-air mixture to the second stage.
GE's first DLN-1 system was tested in 1980. Since then, evolving emissions regulations have continued to drive improvements in the technology. GE's DLN program continues to focus on the development of systems capable of the extremely low NOx levels required to meet today's regulations and to prepare for more stringent restrictions in the future.
GE's DLN technology is certified under ecomagination, GE's commitment to address challenges such as the need for cleaner, more efficient sources of energy, reduced emissions and abundant sources of clean water.
By: John Bartle, DLN Business Segment Leader, GE Energy Services;
Paul Gilmurray, Engineering Manager, GE Energy Services, Asia and
Rachata Sankhavanija, Account Manager, GE Energy Services, Thailand
Media Contact:
Ruthaiwan Sinlapachan / Bhawat Anuwong
Weber Shandwick
Tel.: 0 2343 6000 Ext 067 or 062
Email: ruthaiwan@webershandwick.com; bhawat@webershandwick.com
Photo Show
#01-02 Thaioil Power Plant
#03-05 DLN combustor liner cap and six fuel nozzles
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