WO2012057380A1

WO2012057380A1 - System for reforming biogas using waste heat, and method for reforming biogas using same

Info

Publication number: WO2012057380A1
Application number: PCT/KR2010/007532
Authority: WO
Inventors: 송순호; 김태수; 차효석
Original assignee: 연세대학교 산학협력단
Priority date: 2010-10-29
Filing date: 2010-10-29
Publication date: 2012-05-03
Also published as: KR101136234B1

Abstract

The present invention relates to a system for reforming biogas using waste heat and to a method for reforming biogas using the system. In detail, the system for reforming biogas includes: 1) a gas engine using biogas as a main fuel; 2) a heat exchanger recovering heat from the exhaust gas of the biogas engine in order to increase the temperature of the reforming biogas; and 3) a reformer feeding the reforming biogas into the biogas engine after the reforming biogas heated by means of the heat exchanger is catalytically reformed using a synthesis gas containing hydrogen.

Description

[Correction 18.11.2010] under Rule 26. 규칙 Biogas reforming system and waste gas reforming method using waste heat

The present invention relates to a biogas reforming system using waste heat and a biogas reforming method using the same. Specifically, 1) a gas engine using biogas as a main fuel, and 2) recovering heat from exhaust gas of the biogas engine. A heat exchanger for raising the temperature of the biogas for use, and 3) catalytic reforming the reformed biogas heated through the heat exchanger into a synthesis gas containing hydrogen, and then introducing the reformed gas into the biogas engine. The present invention relates to a biogas reforming system and a reforming method using waste heat including a reformer.

Through the above system and method, it is possible to improve the thermal efficiency of the small gas engine generator, it is possible to implement a biogas fuel reforming system for a small gas engine generator of the on-board type that does not need to supply additional hydrogen for addition.

Large-scale power plants such as thermal power, nuclear power, and hydroelectric power for current electricity generation have advantages in terms of economies of scale, but they generate large amounts of greenhouse gases and are far from consumers, causing transmission losses, and avoiding transmission and substation facilities. Social and environmental negative factors exist.

In order to solve these problems, distributed power supply has started from efforts to reduce energy loss, transmission and distribution facilities by installing small power generation facilities near energy consumers or inside buildings. Distributed power generation is possible even at an economical scale. In particular, in recent years, the development and application of a variety of renewable energy, such as solar, micro gas turbine, gas engine has been considered as a representative type of distributed power generation.

In the case of solar distributed power sources, it can be installed near energy consumers, but the production cost per unit power is relatively high, the efficiency is low, and high frequency is generated by inverter. Distributed power generation using micro gas turbine is small in size and noise. Although it has the advantage of being less and environmentally friendly, there is a limit to commercialization because of the durability problem of the turbine blade rotating at high speed and high installation and maintenance cost per production power compared to the gas engine.

On the other hand, a distributed power source using a gas engine is highly durable and easy to miniaturize, and since it has advantages in terms of cost, it can be commercialized relatively easily. In addition, distributed power generation using a gas engine can recover waste heat and improve work loss to improve thermal efficiency, and there is no great difficulty in producing electric power using renewable energy such as biogas along with fossil fuel such as natural gas. It has advantages.

On the other hand, biogas is attracting attention in terms of waste resource utilization, and many technologies are being developed and researched in domestic and foreign countries on how to utilize it. As part of related research, a demonstration project for distributed power generation system is being developed in Korea to apply electric gas produced from livestock manure to a gas engine.

However, a gas engine generator using biogas as a fuel shows lower overall thermal efficiency and combustion rate than conventional fossil fuels such as natural gas, which can be seen in Table 1 below. Because it interferes with combustion.

Table 1

Composition of biogas
Methane (CH ₄ )	55-65%
Carbon dioxide (CO ₂ )	35-45%
Hydrogen sulfide (H ₂ S)	0-1ppm
Nitrogen (N ₂ )	0-3ppm
Hydrogen (H ₂ )	0-1ppm
Oxygen (O ₂ )	0-2ppm
Ammonia (NH ₃ )	0-1ppm

In order to improve this, various researches have been conducted, and among them, a study of improving the overall combustion efficiency by adding hydrogen having a fast combustion rate to biogas has been actively conducted.

Ilbas et al., 2006, measured the laminar flame rates of hydrogen-air and hydrogen-methane-air mixed gases and reported that combustion rates and flammability increased with increasing hydrogen concentration (Ilbas M, Crayford AP, Yilmaz I, Bowen PJ, Syred N. Laminarburning velocities of hydrogen-ir and hydrogen-methane-air mixture: an experimental study.Int J Hydrogen Energy 2006; 31: 1768--79). In the case of gaseous fuels such as methane, hydrogenation has been found to have a significant effect on engine power.

However, until now, all hydrogen used for hydrogenation research has been supplied from the outside, and since the research has focused on the biogas combustion characteristics when hydrogen is added rather than the production of hydrogen, research on the hydrogen generation method to be added to biogas is It was incomplete.

Accordingly, the present invention has developed a biogas fuel reforming technology for an on-board type small gas engine generator which does not need to separately supply hydrogen for addition while improving the thermal efficiency of the small gas engine generator.

The present invention is to provide a system and method for reforming the waste heat of the exhaust gas to maintain the active temperature of the reforming catalyst, using the same to produce a reformed gas containing hydrogen to enable smooth hydrogen addition to the biogas. The purpose.

In order to achieve the object as described above, the present invention provides a heat exchanger for improving the temperature of the reforming biogas and reforming catalyst by recovering heat from the exhaust gas of the biogas engine. A heat exchanger, and 3) waste heat including a reformer for reforming the reformed biogas heated through the heat exchanger into a synthesis gas containing hydrogen and introducing the reformed gas into a biogas engine. It provides a biogas reforming system using.

On the other hand, in order to achieve the above object, the present invention 1) recovering the exhaust heat of the biogas engine to heat the reforming biogas and reforming catalyst, ii) the hydrogen by using the catalyst as a heated biogas It provides a biogas reforming method using waste heat comprising the step of reforming the synthesis gas included, and iii) introducing the generated reformed gas into the biogas engine.

The reforming system and reforming method may use a burner for supplying additional energy required for the reforming reaction if the recovered exhaust heat is not sufficient to cause the reforming reaction, which burner is a gas burner that burns biogas. , An electric heater or a plasma burner.

In addition, the non-fixed (fixed type), fixed (fixed type), U-type (U-type), cylindrical coil (shell and coil type), so that the exhaust gas and the reforming biogas can be exchanged without mixing Plate type or double pipe type heat exchangers may be used.

The flow rate of the biogas reformed by the reformer is determined according to the amount of hydrogen gas required by the biogas engine and the reforming efficiency of the catalyst, and the type and size of the heat exchanger is adjusted according to the determined flow rate of the reforming biogas. desirable.

In addition, the reforming catalyst may be monolith, pellet, or powder type, and the volume of the reforming catalyst may be determined according to the flow rate of biogas introduced into the catalyst for the reforming reaction.

Reforming catalyst reaction of the reformer may be a mixture of carbon dioxide reforming reaction (CO ₂ reforming), and the reaction is preferred, the carbon dioxide reforming (CO ₂ reforming), and partial oxidation reforming (partial oxidation reforming) to increase the efficiency.

In addition, the reforming catalyst is preferably a precious metal such as platinum (Pt), rhodium (Rh), palladium (Pd), ruthenium (Ru).

By using the biogas reforming system using the waste heat of the present invention, the thermal efficiency of the small gas engine generator can be improved, and the biogas fuel reforming for the small gas engine generator of the on-board type, which does not need to separately supply hydrogen for addition. You can implement the system.

1 is an overall configuration diagram of a biogas reforming system of the present invention.

2 is a cross-sectional view showing an embodiment of a heat exchanger and a reformer constituting the biogas reforming system of the present invention.

3 is a cross-sectional view of a floating type heat exchanger used in the biogas reforming system of the present invention.

4 is a cross-sectional view of a fixed type heat exchanger used in the biogas reforming system of the present invention.

5 is a cross-sectional view of a U-type heat exchanger used in the biogas reforming system of the present invention.

6 is a cross-sectional view of a shell and coil type heat exchanger used in the biogas reforming system of the present invention.

7 is a cross-sectional view of a plate type heat exchanger used in the biogas reforming system of the present invention.

8 is a cross-sectional view of a double pipe type heat exchanger used in the biogas reforming system of the present invention.

In the biogas reforming system according to the present invention, as shown in FIG. 1, 1) a gas engine containing biogas as a main fuel, and 2) recovering heat from exhaust gas of the biogas engine to increase the temperature of the reforming biogas. A heat exchanger, and 3) a reformer for catalytically reforming the reformed biogas heated through the heat exchanger into a synthesis gas containing hydrogen, and then introducing the reformed gas into the biogas engine. .

In addition, the biogas reforming method using the system 1) recovering the exhaust heat of the biogas engine to heat the reforming biogas, ii) reforming the heated biogas into a synthesis gas containing hydrogen using a catalyst And iii) introducing the generated reformed gas into a biogas engine.

In the case of a gas engine generator using biogas as a fuel, carbon dioxide contained in biogas interferes with combustion, resulting in lower overall thermal efficiency and combustion rate than conventional fossil fuels, but adding hydrogen gas having a fast reaction rate to the biogas. This can improve the overall combustion efficiency of the biogas engine.

In order to reform the biogas to generate a synthesis gas including hydrogen, not only a catalyst suitable for the reforming reaction is required, but also the activation temperature must be maintained so that the catalyst reacts with the reforming biogas to cause the reforming reaction.

Most of the catalyst activation temperature is so high as about 400 ℃ to 800 ℃ because a lot of energy input is required, but in the system of the present invention heat exchange to obtain energy for maintaining the catalyst activation temperature from the waste heat of the exhaust gas from the engine Install the machine.

In other words, the biogas flowing into the gas engine is discharged to the outside through the exhaust pipe in the form of high temperature exhaust gas after combustion reaction inside the cylinder of the engine. This can then be fed back into the gas engine, which in turn improves the overall thermal efficiency of the biogas engine.

At this time, the heat exchanger may be used in a variety of forms, preferably as shown in Figures 3 to 8, so that the exhaust gas and the reforming biogas is not mixed with each other, floating type (floating type) A fixed type, U-type, shell and coil type, plate type or double pipe type heat exchanger may be used.

The biogas supplied with heat from the exhaust gas through the heat exchanger is reformed into a synthesis gas including hydrogen gas through a catalytic reforming reaction in the reformer, and the apparatus including the heat exchanger is installed at a point close to the engine for effective heat recovery. It is preferable.

In addition, since the time the biogas stays in the heat exchanger is changed according to the flow rate of the biogas in the heat exchanger, the temperature of the biogas after the heat exchanger is changed according to the flow rate.

Therefore, the flow rate of the biogas required for the reforming reaction is determined according to the required amount of hydrogen reforming gas and the reforming efficiency of the catalyst, and the type and dimensions of the heat exchanger are also affected by the determined flow rate of the biogas.

On the other hand, in order to generate the synthesis gas from the biogas, the presence of the reforming catalyst is essential, and the reformer is a device that supports the reforming catalyst and serves to transfer waste heat of the exhaust gas to the catalyst as well as the heat exchanger.

At this time, the type of catalyst filled in the reformer may vary depending on the type of fuel and reforming, but can be largely divided into a metal catalyst and a noble metal catalyst, and the temperature and reforming efficiency at which the reforming reaction is activated vary for each catalyst.

For example, if the modified primarily to the biogas carbon dioxide reforming (CO ₂ reforming) reaction consisting of methane and carbon dioxide, of a metal catalyst to be commonly used may include nickel (Ni), platinum (Pt) as a noble metal catalyst, Rhodium (Rh), palladium (Pd), ruthenium (Ru) and the like can be used.

In general, when the noble metal catalyst is used compared to the reforming reaction using the metal catalyst, the catalyst activation temperature is relatively low and the active area of the catalyst due to carbon deposition is reduced.

There are three major types of fuel reforming using catalysts. The first is a steam reforming method currently used commercially to obtain high purity hydrogen.

The steam reforming method is mainly used in steam reforming reaction using natural gas, methane (CH ₄ ), carbon dioxide (CO ₂ ), carbon monoxide (CO), hydrogen (H ₂ ), water (H ₂ O), carbon (C Components such as) may be present in the reaction. Reactions that may occur from the steam reforming reaction are as follows.

TABLE 2

Scheme	Reaction heat
(1) CH ₄ + H ₂ O ↔ CO + 3H ₂	ΔH = 49.2 kcal / mol
(2) CO + H ₂ O ↔ CO ₂ + H ₂	ΔH = -9.8 kcal / mol
(3) CH ₄ + 2H ₂ O ↔ CO ₂ + 4H ₂	ΔH = 39.4 kcal / mol
(4) CH ₄ + CO ₂ ↔ 2CO + 2H ₂	ΔH = 59.0 kcal / mol
(5) CH ₄ + 3CO ₂ ↔ 4CO + 2H ₂ O	ΔH = 78.8 kcal / mol
(6) CH ₄ ↔ C + 2H ₂	ΔH = 17.9 kcal / mol
(7) 2CO ↔ C + CO ₂	ΔH = -41.4 kcal / mol
(8) CO + H ₂ ↔ C + H ₂ O	ΔH = -31.3 kcal / mol
(9) CO ₂ + 2H ₂ ↔ C + 2H ₂ O	ΔH = -21.5 kcal / mol
(10) CH ₄ + 2CO ↔ 3C + 2H ₂	ΔH = -44.8 kcal / mol
(11) CH ₄ + CO ₂ ↔ 2C + 2H ₂ O	ΔH = -3.7 kcal / mol

Recent studies have reported that (1) to (3) are endothermic reactions (1) and (3), and that exothermic reactions can occur under steam reforming conditions. to be.

The steam reforming process is a unit reaction process that primarily produces high concentrations of hydrogen by reforming natural gas from which sulfur is removed, and has a higher yield of hydrogen production per mole of methane than the partial oxidation and autothermal reforming processes. It can be called a method.

However, due to the slow reaction speed due to the equilibrium reaction, the process size should be large and the response characteristics to the steady state to the load fluctuations are slow. As a strong endothermic reaction, the forward reaction is advantageous only at high temperature and low pressure conditions.

The second reforming process is a partial oxidation reforming method, in which a synthesis gas is obtained by supplying oxygen of less than the stoichiometry required for complete combustion with fuel at the same time, accompanied by a weak exothermic reaction by the partial oxidation reaction. .

Therefore, unlike the steam reforming process, the partial oxidation reforming process does not necessarily require an external heat source, so the reactor is relatively small in size and has excellent initial start-up and load response characteristics. However, the hydrogen production efficiency is relatively low compared to other processes. Has its drawbacks. The general partial oxidation scheme is as follows.

CH ₄ + 1 / 2O ₂ → CO + 2H ₂ ΔH = -9 kcal / mol

Finally, the CO ₂ reforming process is being actively conducted as part of an effort to chemically convert global warming gas carbon dioxide into a more useful compound, which is a synthesis gas containing a higher concentration of carbon monoxide than a conventional steam reforming reaction. Can be obtained. A general carbon dioxide reaction is as follows.

CH ₄ + CO ₂ → 2CO + 2H ₂ ΔH = 59 kcal / mol

In the case of biogas, since carbon dioxide is already contained in the gas, it is easy to induce a carbon dioxide reforming reaction. However, since the carbon dioxide reforming reaction is a strong endothermic reaction and the activation temperature of the catalyst used is relatively high, other reforming reactions, such as partial oxidation reforming reactions, may be selectively carried out together.

The catalyst can be used in various forms such as monolith, pellet, powder type. In addition, the size and volume of the catalyst may be determined in consideration of the flow rate of the biogas flowing into the catalyst for the reforming reaction, in which case the concept of Gas Hourly Space Velocity (GHSV) may be used. The equation of gas space velocity is:

GHSV = F _v / V _r [L / hr] (V _r : volume of catalyst, F _v : volume feed rate of biogas)

On the other hand, when the waste heat is recovered from the high-temperature exhaust gas discharged from the engine and applied to the biogas reforming reaction, when additional energy supply is required, a separate burner may be installed to supply energy. The position of the gas burner is determined in consideration of effective heat transfer, and may be formed to heat the heat exchanger and the reformer as shown in FIG. 1, or may be formed directly on an exhaust gas line entering the heat exchanger as shown in FIG. 2. have.

The burner may be a gas burner that heats exhaust gas, heat exchanger, reformer, etc. with heat released by mixing and burning biogas, oxygen, and air,

In addition to the gas burner, various types of burners such as an electric heater and a plasma burner may be used.

By using the biogas reforming system having the above-described configuration, it is possible to improve the thermal efficiency of the small biogas engine, and to implement the on-board compact biogas fuel reforming system, which does not need to separately supply hydrogen for addition. have.

The present invention is not limited to the above specific embodiments and descriptions, and various modifications can be made by those skilled in the art without departing from the gist of the invention as claimed in the claims. Such variations are within the protection scope of the present invention.

Claims

1) a gas engine using biogas as the main fuel, 2) a heat exchanger for recovering heat from exhaust gas of the biogas engine to raise the temperature of the reforming biogas, and 3) heated through the heat exchanger. A biogas reforming system using waste heat including a reformer for reforming the reforming biogas into a synthesis gas containing hydrogen and introducing the reformed gas into a biogas engine.

The biogas using waste heat according to claim 1, further comprising a burner for supplying additional energy required for the reforming reaction when the exhaust heat recovered through the heat exchanger is not sufficient to cause the reforming reaction. Reforming system.

The biogas reforming system using waste heat according to claim 2, wherein the burner is a gas burner, an electric heater or a plasma burner for burning the biogas.

The heat exchanger of claim 1, wherein the heat exchanger is a floating type, a fixed type, a U-type, or a cylindrical coil type so that the exhaust gas and the reforming biogas are not mixed. Biogas reforming system using waste heat, characterized in that (shell and coil type), plate type (double type) or double pipe type (double pipe type).

The biogas reforming system using waste heat according to claim 1, wherein the flow rate of reforming biogas flowing into the reformer is determined according to the amount of hydrogen gas required in the biogas engine and the reforming efficiency of the catalyst.

The biogas reforming system using waste heat according to claim 5, wherein the type and size of the heat exchanger are adjusted according to the determined flow rate of the reforming biogas.

The reforming catalyst of claim 1, wherein the reforming catalyst is of a monolith, pellet, or powder type, and the volume of the reforming catalyst is determined according to the flow rate of biogas introduced into the catalyst for the reforming reaction. Biogas reforming system using waste heat, characterized in that.

According to claim 1, wherein the reforming reaction takes place in the reformer the carbon dioxide reforming (CO ₂ reforming) reaction or a carbon dioxide reforming bio using the waste heat, characterized in that mixing the reaction of (CO ₂ reforming), and partial oxidation reforming (partial oxidation reforming) Gas reforming system.

The biogas reforming integrated system using waste heat according to claim 1, wherein the reforming catalyst is a precious metal such as platinum (Pt), rhodium (Rh), palladium (Pd), ruthenium (Ru).

1) recovering the exhaust heat of the biogas engine to heat the reforming biogas;

ii) reforming the heated biogas into a synthesis gas containing hydrogen using a reforming catalyst; And

iii) introducing the generated reformed gas into a biogas engine;

Biogas reforming method using waste heat comprising a.

The method according to claim 10, wherein if the exhaust heat recovered from the biogas engine is not sufficient to cause a reforming reaction, supplying additional energy for the reforming reaction through a burner to the reforming biogas or reforming catalyst. Biogas reforming method using waste heat characterized in that.

12. The method of claim 11, wherein the burner is a gas burner, an electric heater or a plasma burner for burning the biogas.

11. The method of claim 10, wherein the heating of the reforming biogas using the exhaust gas is floating (fixed type), fixed (fixed type), U-type (U-type), cylindrical coil type (shell and coil type), flat plate A biogas reforming method using waste heat, characterized in that it is not mixed with each other by a plate type or a double pipe type heat exchanger.

The method of claim 10, wherein the flow rate of the reforming biogas is adjusted according to the amount of hydrogen gas required by the biogas engine and the reforming efficiency of the catalyst.

15. The method of claim 14, wherein the type and size of the heat exchanger is adjusted according to the determined flow rate of the reforming biogas.

The reforming catalyst of claim 10, wherein the reforming catalyst is of a monolith, pellet, or powder type, and the volume of the reforming catalyst is determined according to the flow rate of the biogas introduced into the catalyst for the reforming reaction. Biogas reforming method using waste heat, characterized in that.

The method of claim 10 wherein reforming the reforming reaction of the bio-gas carbon dioxide using the above catalyst (CO ₂ reforming) reaction or a carbon dioxide reforming (CO ₂ reforming), and the partial oxidation reforming heat characterized by mixing the reaction of the (partial oxidation reforming) Biogas reforming method using.

The method of claim 10, wherein the reforming catalyst is a precious metal such as platinum (Pt), rhodium (Rh), palladium (Pd), ruthenium (Ru).