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Firing up on naphtha

Firing up on naphtha

Japanese chemical company, Tosoh, is constructing a LM6000 gas turbine-based power plant at its Yokkaichi facility. Fuelled with byproducts of the naphtha cracking process, this captive plant will be integrated with a new naphtha cracking furnace. Significantly, it will be the first plant to use an LM6000 running on naphtha.

Kazunobu Ogiso,

S&S Technical Services Japan, Ltd.,

Terrence Sharp,

GE Industrial AeroDerivative Gas Turbines,

Tokyo, Japan

In May 1999, a GE LM6000 aeroderivative gas turbine will begin commercial operation burning a combination of methane and hydrogen fuel – the byproducts from the naphtha cracking process at a petrochemical plant in Yokkaichi, Japan.

This captive power plant will be a unique application for the LM6000, not only because of the fuel, but also due to the integration of the power plant with the naphtha cracking plant. Tosoh, the owner of the petrochemical plant, expects to see a significant increase in the naphtha cracking plant`s overall thermal efficiency and an increase in production capacity as a result.

Captive power generation currently accounts for a significant portion of Japan`s overall electricity business. The Japanese government`s policy on the construction of new thermal power plants is classified into two categories:

à‚-Short lead time power plant (SLT power) – completion of the plant within ten years

à‚-Long lead time power plant (LLT power) – completion of the plant longer than ten years.

All SLT power must be purchased by public tender, and none of Japan`s power utilities can compete. All LLT power including replacement power must also be purchased by public tender, but in contrast, the tender is open to power utilities as well as independent power producers (IPPs). However, no public utilities can construct LLT power plants unless tender can be obtained through competition with other power utilities and IPP developers.

A changing market

The Japanese government is currently considering deregulation of the country`s electricity retail business. A final report is expected to be presented to the government by the Special Committee in December 1998.

To comply with the Japanese government`s commitment to reduce CO2 emissions by six per cent until 2010, the central and local governments have imposed very severe environmental regulations on power generating plants. With this in mind, gas turbine combined cycle power plants using clean burning fuels will probably account for the majority of future SLT power projects in this country. Table 3 provides a ten year forecast of the Japanese power market.

The total captive power capacity for the coming ten years will be maintained or slightly increased. The 8000 MW forecasted in Table 3 will replace existing captive power plants due to life time and environmental issues. It is likely that almost all new captive power plants will also be based on combined cycle cogeneration gas turbine technology.

Expanded facilities

Tosoh was established in 1935, and is headquartered in Tokyo, Japan. The worldwide company has 4600 employees, and approximately 80 per cent of its sales are generated in Japan. Its Petrochemicals Group produces olefin products such as ethylene, propylene and polyolefin products. Other basic groups within the company produce sodium hydroxide and sodium carbonate, and cements such as Portland fly-ash and Portland blast-furnace slag.

The company also produces fine chemical products, scientific and diagnostic instruments and systems and specialty materials and electronics products.

Tosoh is expanding its Yokkaichi naphtha facility which currently has 13 cracking furnaces with a total production capacity of 400 000 t of ethylene per year. The ex- panded plant will feature a simple cycle power plant where heat recovered from the gas turbine exhaust will be used for the cracking furnaces.

TEC of Japan and Lummus of the USA are handling the engineering and construction of the naphtha cracking plant expansion and the heat recovery system for the gas turbine exhaust. Mitsui Engineering & Shipbuilding (MES) of Tokyo is responsible for the engineering, procurement and construction of the power generation portion of Tosoh`s naphtha cracking plant expansion.

The GE Power Systems business unit, S&S Energy Products, will supply the LM6000 gas turbine generator as a subcontractor to MES. The LM6000 will be manufactured by GE Industrial Aero- Derivative Gas Turbines (GE-IAD) at its Evendale, OH facility.

Tosoh selected the LM6000 for this project because of its proven performance record in various power generation applications. Currently there are over 115 LM6000 gas turbines operating throughout the globe. In addition, S&S is no stranger to the Japanese power market. There are currently two S&S supplied LM2500 gas turbine generators operating at two separate power plants in Ibaragi and Takasaki, Japan.

Tosoh currently uses the byproduct gas of the naphtha cracking process for the naphtha cracking furnaces. With the new power plant, the byproduct gas will be used to fuel the LM6000 gas turbine generator set to produce 41 MW of electricity. The electrical power generated by the gas turbine will be used at the Yokkaichi facility. The exhaust heat from the gas turbine will be recovered to supply heat to the new naphtha cracking furnace as well as to the existing furnaces. Total plant capacity will increase by 25 per cent to 500 000 t of ethylene per year.

Tosoh expects the Yokkaichi facility`s overall thermal efficiency to improve considerably with the new naphtha furnace and the captive power arrangement.

Packaging design

The LM6000 shares 90 per cent commonality with GE`s CF6-80C2 aircraft engine, and is a unique aeroderivative in that its low pressure turbine can be directly coupled to its load without using a separate power turbine. This concept improves the simple cycle efficiency, and reduces the gas turbine`s cost and unit size.

The LM6000 low pressure rotor consists of a five stage low pressure compressor and a five stage low pressure turbine connected by means of a mid-shaft, which extends through the centre of the engine. The high pressure rotor consists of a 14 stage high pressure compressor and a direct coupled, two stage high pressure turbine.

The LM6000 is designed to operate at an output shaft speed of 3600 r/min for electrical power generation. The HP rotor speed varies from 6000 r/min to 10 600 r/min over the operating power range from idle to full power. A reduction gearbox reduces shaft speed from 3600 r/min to 3000 r/min in 50 Hz applications. The gas turbine is equipped with three systems which control airflow to achieve the desired performance characteristics.

Variable inlet guide vanes in front of the low pressure compressor modulate airflow entering the flowpath. Variable bleed valves between the low and high pressure compressors allow some airflow to be dumped at low power conditions.

Six stages of variable stator vanes on the high pressure compressor stage maintain high efficiency over the power range.

S&S uses standardized package designs to shorten manufacturing time. This enables a power plant to be operational shortly after the signing of a contract. All packages are factory assembled and tested at full load prior to shipment to reduce performance risks for the owner and operator.

The Brush generator is designed to accommodate full gas turbine power output over the full ambient air temperature range. The generator is sized larger than the turbine output to accommodate future ratings increases. The gas turbine is controlled by Woodward Governor`s NetCon 5000 controls.

GE recently announced an enhancement to the already-popular LM6000 ideal for customers that want more power: a new spray intercooling system which is expected to increase this aeroderivative gas turbine`s power output by at least nine per cent. Known as the LM6000 Sprint (SPRay INTercooling), this product enhancement also will reduce simple and combined cycle life cycle costs.

Benefits of the Sprint system include:

à‚-Nine per cent power boost at ISO conditions

à‚-Seventeen per cent increase in power on hot days (greater than 80 degreesF) with some efficiency improvement

à‚-Elimination of inlet chillers for most installations.

The Sprint system

The Sprint cooling lowers the high pressure compressor inlet temperature, which in turn effectively lowers the compressor discharge temperature. The system consists of an interstage mist injection system which cools the low pressure booster discharge air. Water is injected into the airflow path through a series of 24 air-assisted spray injection nozzles located in the engine front frame.

Air for the system is supplied from the engine`s eighth stage customer bleed extraction port.

By using the Sprint spray intercooling system, the compressor pressure ratio can be increased and additional air can be directed through the compressor in order to increase the gas turbine`s output characteristics.

In addition to being offered for production LM6000 PC units, the Sprint system will be available for those LM6000 PA models that have already been retrofitted using an LM6000 uprate kit.

Market opportunities

Industrial captive power is on the rise in Japan, and numerous opportunities are present for environmentally friendly gas turbine-based power plants such as that at Yokkaichi. S&S expects to deliver the LM6000 gas turbine generator set to the site in late 1998.

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Figure 1. Map of Japan showing the location of Tosoh`s Yokkaichi facility

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Figure 2. The Yokkaichi facility

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