JPH0286926A - Effective processing method for boil-off gas generating out of liquefied natural gas and compound power plant using lng for fuel - Google Patents

Abstract

PURPOSE:To utilize boil-off gas so effectively without entailing any environmental pollution by securing electric generating power with a fuel cell in using the BOG generating from an LNG storage tank of a gas turbine power plant, making LNG as fuel. CONSTITUTION:LNG 2 in a storage tank 1 is being evaporated little by little due to heat input out of the outside, and this generated gas is called 'BOG'. In addition, the LNG 2 is fed to a carburetor 7 by a booster pump 6, gasified with seawater 100, and fed to a gas turbine power plant 10. The LNG further supplied is ignited in a combustor 50, driving a turbine 54, and thereby a generator 56 is rotated for power generation. In this case, a low pressure fuel system 22 extracting the BOG 3 is intensified in pressure by a boost compressor 8, thus the BOG 3 is fed to a fuel cell 9. Then, this fuel cell 9 generates electric power in using the BOG as fuel.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention effectively utilizes boil-off gas (hereinafter referred to as BOG) that evaporates from liquefied natural gas (hereinafter referred to as LNG) used as fuel for power generation plants. The present invention relates to a combined power generation plant created to be suitable for carrying out the above-mentioned effective treatment method.

[Conventional technology]

Regarding the technology of using LNG as fuel and driving a generator with a gas turbine, the document "About liquefied natural gas (LNG)" (Tokyo Electric Power Company Takatsu Thermal Power Plant Pamphlet 1~) is publicly known.

FIG. 3 is a schematic system diagram depicting the configuration of a known LNG gas turbine power plant.

The LNG storage tank 1 is a cylindrical tank covered with a hemispherical canopy 4, and is composed of an inner tank for storing LNG 2, a heat insulating material, and an outer tank for holding these (none of which are shown). .

LNG2 in the storage tank 1 is vaporized little by little due to heat input from the outside, and this generated gas is called BOG3.

The BOG 3 described above remains in the space between the liquid level of the LNG 2 and the canopy 4.

It is necessary to constantly consume BOG3 so that the pressure inside the storage tank 1 does not rise abnormally due to BOG3.

On the other hand, the LNG2 is sent to the vaporizer 7 by the boost pump 6, gasified using seawater 100, and supplied to the gas turbine power plant 10.

The supplied LNG is combusted in a combustor 50 to drive a turbine 54 and rotate a generator 56. 52 is a compressor that supplies combustion air, and usually the combustor 5
0. The compressor 52 and the turbine 54 are collectively referred to as a gas turbine.

150 in the figure is a flow control valve that controls the LNG gas flow rate;
120 is a check valve, and 140 is a main valve.

The pressure of the BOG 3 is increased by the boost compressor 8 and the check valve 1
10. It is supplied to the combustor 50 via the main valve 130 and burned.

[Problem to be solved by the invention]

The BOG mentioned above tends to contain a large amount of nitrogen. The reason is as follows.

For example, assume that LNG contains 0.5% nitrogen.

The boiling point of nitrogen is -196°C, which is 33°C lower than the boiling point of -163°C of methane, the main component of LNG.

Nitrogen evaporates first, methane evaporates later.

As a result, BOG contains more nitrogen than methane, exceeding 12.5% (volume percentage).

Currently, in Japan, a lean premix combustion method using a dry low NOx combustor is often used to reduce the NOx generation rate. There is a problem of unstable combustion when combustion is performed.

FIG. 2 is a chart showing the relationship between nitrogen content (volume) and amount of heat generated.

Naturally, the amount of heat generated decreases as the nitrogen content increases, but there is also the problem that if the nitrogen content exceeds 12.5%, the combustion state becomes unstable.

Unstable combustion causes problems such as the generation of carbon monoxide and flame vibration, which in severe cases can lead to misfires.

Meanwhile, gas turbine power plants are shut down on weekends in response to weekly changes in electricity demand. In this case, one or two of the several gas turbines must be operated to consume the BOG that is constantly generated. In such cases, it is difficult to use a lean premix combustion type dry low NOx combustor.

In addition, when using a conventional type of combustor, NO in the exhaust gas
x concentration becomes high, making it impossible to satisfy environmental regulations.

The present invention has been made in view of the above circumstances, and provides a method for obtaining electrical energy by effectively utilizing BOG without polluting the environment, and a combined power generation plant suitable for implementing the above method. The purpose is to

[Means to solve the problem]

The method of the present invention created to achieve the above object is as follows:
BOG generated from LNG is fed to a fuel cell, which uses the BOG as fuel to generate electricity.

When carrying out this method, it is also possible to perform power generation by the fuel cell only when the nitrogen content exceeds 12.5%, which is the unstable combustion region, as explained with reference to FIG. This is because BOG can be supplied to the gas turbine when it is below 12.5%, which is the stable combustion range.

Furthermore, the combined power generation plant of the present invention created to achieve the above object includes a gas turbine device that forcibly vaporizes LNG and generates power by burning it, and a fuel cell that generates power using BOG as fuel. It will be attached.

When implementing the combined power generation plan 1 of the present invention, if a boiler that recovers the exhaust heat of the gas turbine to generate steam and a steam turbine that is driven by the steam generated by the boiler are installed together, the power generation plant can be used as a power generation plant. Overall efficiency is improved.

[Effect]

If BOG generated from LNG is supplied to a fuel cell and the fuel cell generates electricity as in the method of the invention described above, BOG can be used effectively without polluting the environment, regardless of the nitrogen content of BOG. can. LNG, which occupies most of the amount in the storage tank after evaporating BOG, can be burned with low pollution in a lean premix combustion type low NOx combustor to drive a gas turbine.

In addition, like the power generation plant described above, if a fuel cell that feeds BOG to a fuel cell to generate electricity and a gas turbine device that generates electricity by forcedly vaporizing and combusting LNG are installed together,
The method of the invention described above can be easily implemented.

〔Example〕

Next, a first embodiment of the combined power generation plant according to the present invention will be described.
The diagram will be explained.

This embodiment is an improvement of the conventional power plant shown in FIG. 3 by applying the present invention.

A high-pressure fuel system 20 (pressure approximately 20 kg/cdg) that pumps LNG in a storage tank 1 with a temperature rising pump 6 is gasified by a vaporizer (open rack vaporizer) 7 using seawater 100, and is then transferred to a gas turbine power plant 10. The power generation system that supplies the power generation system has a configuration similar to that of the conventional example shown in FIG.

On the other hand, the low pressure fuel system 22 that extracts the BOG 3 is boosted to approximately 7 kg/cdg by the boost compressor 8 and is supplied to the fuel cell 9.

The fuel cell 9 uses the supplied BOG as fuel to generate electricity (power generation) without emitting almost any pollutants.

The amount of BOG generated above varies slightly depending on the outside temperature, but it is generated continuously. From the viewpoint of equipment reliability, fuel cells are required to operate without drastic load changes.

From this relationship, it is convenient for the fuel cell to generate electricity using BOG as fuel.

On the other hand, the gas turbine power plant 10 is operated using the high-pressure fuel 20 as fuel and does not need to process BOG, so it can be started up in response to intermediate load operation that requires shutdown on weekends, for example.
A stop operation can be performed. Moreover, BOG with high nitrogen content
Since the premixed low NOx combustor is not supplied with low NOx, lean premixed low NOx combustors can easily be used to provide low NOx operations that meet prescribed environmental standards.

Although not shown, if the nitrogen content of BOG is 12.5% or less, it is also possible to feed the BOG to the combustor 50 and combust it. This is because if the nitrogen content is 12.5% or less, stable combustion of BOG can be achieved as explained with reference to FIG.

Furthermore, although not shown, a boiler that collects exhaust gas from the gas turbine 54 to generate steam, and a steam turbine driven by the steam generated by the boiler are provided.
The overall thermal efficiency of the combined power plant consisting of the gas turbine power plant 10 and the fuel cell 9 can be further improved.

〔Effect of the invention〕

As explained above, according to the method of the present invention, electric output is obtained by a fuel cell using the BOX generated from the LNG storage tank of a gas turbine power generation plant that uses LNG as fuel, thereby eliminating the risk of polluting the environment. BOG can be used effectively.

Further, according to the combined power generation plant of the present invention, there is provided a power generation system that forcibly vaporizes and burns LNG to drive a gas turbine and rotate a generator, and an electrical output system that uses BOG generated from the LNG as fuel. By installing a power generation system using a fuel cell that generates BOG, it is possible to effectively utilize BOG to obtain electrical energy without polluting the environment.

When the above BOG treatment method is implemented using the above power plant, the gas turbine power plant can be shut down on weekends and the internal load of the power plant can be purchased by the fuel cell. Furthermore, since a lean premix combustion type low NOx combustor can be employed as the combustor of the gas turbine, low NOx gas turbine power generation can be performed. On the other hand, fuel cells are continuously supplied with BOG and can be operated at a nearly constant load at all times, so the temperature and pressure inside the cell are kept constant, allowing for highly reliable and durable operation. .

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an embodiment of a combined power generation plant using LNG as fuel according to the present invention. FIG. 2 is a chart showing the relationship between the nitrogen content in BOG and the amount of heat generated. FIG. 3 is a system diagram showing a conventional LNG power generation plant. 1...LNG storage tank, 2...LNG, 3...BO
G, 4... Canopy, 6... Boost pump, 7... Carburizer, 8... Boost compressor, 9... Fuel cell, 10...
...Gas turbine power plant, 50...Combustor, 52...
・Compressor, 54... Turbine, 56... Generator, 1
00... Seawater, 110.120... Check valve, 130
゜140... Main valve, 150... Steam flow control valve.

Claims (1)

[Claims] 1. L of a gas turbine power plant using LNG as fuel
In a method for treating BOG generated from an NG storage tank,
An effective method for processing BOG generated from LNG, characterized in that the BOG described above is fed to a fuel cell by a boost compressor, and the fuel cell generates electricity using the BOG as fuel. 2. If the volume content of nitrogen gas in the BOG generated from the LNG storage tank exceeds 12.5%, the BOG is fed to a fuel cell by a boost compressor to generate electricity. , An effective method for treating BOG generated from LNG as claimed in claim 1. 3. In power plants that use LNG as fuel, LNG
a vaporizer to which the LNG in the LNG storage tank is fed; a combustor that burns the gas generated in the vaporizer; and a turbine driven by the combustion gas generated in the combustor. , a compressor and a generator driven by the turbine;
A power generation plant that uses LNG, characterized in that it is equipped with a boost compressor that feeds BOG generated in the LNG storage tank to a fuel cell, and a fuel cell that generates electricity using the BOG as fuel. A combined power generation plant that uses fuel. 4. The gas turbine is equipped with a steam turbine, and a boiler that recovers the heat of the exhaust gas of the gas turbine to generate steam, and supplies the steam generated by the boiler to the steam turbine. The combined power generation plant using LNG as fuel according to claim 3, further comprising a pipe line.