JPH05287284A - Process for reforming liquefied natural gas - Google Patents

Abstract

PURPOSE:To obtain efficiently a gas turbine fuel which does not evolve CO2 during combustion by reforming liquefied natural gas successively in a reformer and by the shift reaction, separating CO2 from the reformed gas, and liquefying the CO2 by the cold heat of the liquefied natural gas. CONSTITUTION:After the recovery of the cold heat of liquefied natural gas (hereinafter referred to an LNG) in cold-heat-recovery heat-exchangers 1 and 2, the LNG is gasified in an LNG vaporizer 3 and fed to a reformer 4. Steam is fed to the reformer 4 at the same time to reform CH4 in the feed gas to H2 and CO. Then, the reformed gas is introduced into a high-temperature CO shift reactor 5 and a low-temperature shift reactor 6 to reform the CO through the shift reaction with steam to H2 and CO2. Thereafter, the reformed gas is fed into PSA11 for CO2 absorption to separate and remove the CO2 which is then liquefied in a CO2 liquefier 13 making use of the cold heat of the LNG. On the other hand, the reformed gas, from which CO2 has been separated, is used as a fuel in a gas turbine 15.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for reforming liquefied natural gas.

[0002]

2. Description of the Related Art Conventionally, a part of carbon dioxide gas in combustion exhaust gas has been concentrated and separated and collected in a gas, liquid or solid state, but the carbon dioxide gas is practically not collected. , Was released to the atmosphere as it was. Half of the carbon dioxide released into the atmosphere is absorbed by the ocean,
The rest remains in the atmosphere, and due to the increase in the amount of combustion exhaust gas in recent years, absorption by the ocean etc. cannot keep up. Therefore, the amount of carbon dioxide in the atmosphere has increased, and in recent years, an increase in atmospheric temperature called the greenhouse effect has become a problem.

As a method for separating carbon dioxide gas, there are an absorption method and an adsorption method. Table 1 shows an example of the absorption method. Generally, carbon dioxide gas is absorbed into the absorbing solution by pressurization, and the absorbing solution is regenerated by lowering the pressure or heating in the regeneration step.

[0004]

[Table 1]

In the adsorption method as well, carbon dioxide gas is adsorbed on the adsorbent by pressurization, and the adsorbent is regenerated by reducing the pressure in the regeneration step. This adsorption / regeneration process is discontinuous and involves changes in pressure and temperature.

On the other hand, recently, natural gas is liquefied and transported.
The construction of a power plant by high-efficiency gas turbine combined power generation that stores and uses this as fuel is being promoted. The cold heat of LNG released when this liquefied natural gas (LNG) is used as gas fuel is being promoted. A method of solidifying and recovering carbon dioxide as dry ice by using it has been proposed.

In the method proposed in Japanese Patent Laid-Open No. 61-40808, low temperature liquefied natural gas is supplied into a cooling pipe provided in a carbon dioxide cooler (heat exchanger), and carbon dioxide gas is provided outside the cooling pipe. Exhaust gas containing is distributed. At this time, due to the cold heat of the low temperature liquefied natural gas in the cooling pipe,
Carbon dioxide gas outside the cooling pipe is cooled by indirect heat exchange,
It solidifies and adheres to the pipe surface. This is sometimes scraped off and collected.

There is also a proposal of a method for solidifying and separating carbon dioxide gas by directly mixing the gas cooled to a low temperature by exchanging heat with the cold heat of LNG and the exhaust gas containing carbon dioxide gas.

[0009]

The concentration of carbon dioxide gas in the combustion exhaust gas is very low, about 5 to 10 mol%, and the method of separating and recovering a minute amount of CO ₂ from a large amount of gas is very energy efficient. Is bad and technically very difficult.

The present invention seeks to provide a process capable of recovering CO ₂ generated with consideration of the above prior art, to suppress the occurrence of CO ₂ expediently.

[0011]

The present invention relates to a method for reforming liquefied natural gas as a fuel for a gas turbine, wherein the liquefied natural gas is reformed by a reformer into a gas containing H ₂ and CO as main components, and further, After reforming CO into H ₂ and CO ₂ by a shift reaction with steam, it is separated from the reformed gas.
A method for reforming liquefied natural gas, characterized in that the removed CO ₂ is liquefied by the cold heat possessed by the liquefied natural gas.

Hereinafter, the present invention will be described more specifically with reference to FIG. LNG is generally about -160 to -1
It is transported to the power plant at a low temperature of 70 ℃. After the cold heat held by the LNG is recovered by the heat recovery heat exchangers 1 and 2, the LNG vaporizer 3 vaporizes it from liquid to gas and supplies it to the reformer 4.

On the other hand, steam is supplied to the reformer 4, and about 80% or more of CH _{4 in} the raw material gas is reformed into H ₂ and CO by the following reaction at about 800 to 900 ° C. CH ₄ + H ₂ O → 3H ₂ + CO Further, the reformed gas is a high temperature CO shift reactor 5 and a low temperature C
It is introduced into the O shift reactor 6 and reformed into H ₂ and CO ₂ by the following reaction at about 300 to 400 ° C. CO + H ₂ O → H ₂ + CO ₂

After the heat of the reformed gas is recovered by the waste heat recovery boiler 7 and the gas cooler 8, the drain separator 9 and the PSA for dehumidification are used.
PSA for CO ₂ separation by separating and removing H ₂ O at 10
Be led to. Here, the CO ₂ and the unreformed CH ₄ in the reformed gas are separated and about 20 kg /
After being pressurized to cm ² or more, the CO ₂ liquefaction device 13 changes the phase from a gas to a liquid and is then recovered in the storage tank 14 as a liquid.

On the other hand, the reformed gas containing H ₂ as a main component after separating CO ₂ and unreformed CH ₄ from the gas turbine 15
Used as fuel in. The gas generated at this time is H ₂ O
Only. H ₂ + O ₂ → H ₂ O

The exhaust gas from the gas turbine is further discharged from the chimney 18 after the waste heat is recovered by the steam turbine 16 and the heat recovery heat exchanger 17.

By the above method, the carbon-free gas after the carbon in the raw material is separated and recovered as liquid CO ₂ by reforming without directly burning it is used as the fuel.

[0018]

[Operation] (1) The main component of LNG is CH_FourAnd H₂O
Reforms carbon to CO by reforming reaction with. CH_Four+ H₂O → 3H₂+ CO (2) CO and H₂O reforming reaction causes H₂And CO₂Live
To achieve. CO + H₂O → H₂ + CO₂ (3) Generated CO₂Fuel gas (H₂)
To remove from. Generally, air is used to correct LNG.
Compared to the case of direct combustion, N in the combustion exhaust gas ₂Contains
Because there is no CO₂High concentration, CO₂Low separation energy
Yes. (4) H₂In the combustion reaction of CO₂Does not generate. Obey
CO in the combustion exhaust gas₂Does not mix. H₂ + O₂ → H₂O

[0019]

EXAMPLE Table 2 shows an example of the material balance of a plant of 1,400 MW scale, which was carried out by the process flow of the present invention shown in FIG. In Table 1, items 1 to 3 indicate the points shown in FIG.

[0020]

[Table 2]

[0021]

As described above, according to the present invention, (1) the carbon in the raw material is separated and removed in a high concentration state, so that the carbon separation efficiency is good, and (2) the carbon is produced by the reforming reaction. H
_Since CO ₂ is not generated in the combustion of No. _2, there is a feature that there is no generation of CO ₂ which is currently a problem in global environmental pollution, and this method can be advantageously applied to an industrial scale device.

[Brief description of drawings]

FIG. 1 is a flow chart of one embodiment of a process showing the method of the present invention.

Claims (1)

[Claims] 1. A method for reforming liquefied natural gas as a fuel for a gas turbine, wherein the liquefied natural gas is reformed by a reformer into a gas containing H ₂ and CO as main components, and C
After reforming the H ₂ and CO ₂ by a shift reaction with steam to O, liquefied natural gas, characterized in that the liquefied by cold energy possessed by the CO ₂ liquefied natural gas separated and removed from the reforming gas Modification method.