Method for producing liquid fuel, and liquid fuel

Abstract

The present invention provides: a method for producing a liquid fuel, with which it is possible to achieve a liquid fuel that has improved ignitability with less environmental impact; and a liquid fuel.　By this method for producing a liquid fuel according to the present disclosure, a liquid fuel, in which methanol and dimethyl ether are mixed with each other, is produced by carrying out: a liquefaction step in which, for example, dimethyl ether that is obtained by dehydrating methanol is liquefied, for example, by applying a pressure of 1 MPa or more; and a mixing step in which liquid methanol and the liquefied dimethyl ether are mixed, for example, at a mass ratio of 8:2 to 2:8.

Description

Liquid fuel manufacturing method and liquid fuel

[0001] The present invention relates to a method for producing a liquid fuel using methanol and dimethyl ether, and to the liquid fuel.

[0002] Heavy oil is used as fuel to drive diesel engines installed on ships and the like. Heavy oil is produced from fossil fuels and emits soot when burned, which places a high burden on the environment. Therefore, under industrial policies aimed at achieving carbon neutrality, it is likely that its use will eventually be restricted. Therefore, there is a demand for the development of new fuels that have a low environmental impact, even for marine engines. One such new fuel that has attracted attention is methanol, which can be produced using carbon dioxide as a raw material and can significantly reduce soot emissions (see, for example, Patent Document 1).

[0003] Methanol has an ignition point of approximately 470°C, making its poor ignition a problem when used as an engine fuel. Therefore, fuels with low ignition points, such as heavy oil, are sometimes used as pilot injection fuel for ignition. Pilot injection is the injection of a small amount of fuel at the end of the compression stroke in a diesel engine. The combustion of the pilot-injected fuel raises the temperature in the combustion chamber, shortening the ignition delay of the fuel supplied by the main injection.

[0004] Japanese Patent Application Publication No. 09-046817

[0005] However, the heavy oil used as pilot injection fuel is produced from fossil fuel and emits soot when burned, which poses a problem of insufficient reduction in environmental impact.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a method for producing a liquid fuel and a liquid fuel that can reduce the environmental load while improving ignition performance.

[0007] In order to solve the above problems, the method for producing liquid fuel disclosed in the present application is characterized by carrying out a liquefaction step of liquefying dimethyl ether by pressurization, and a mixing step of mixing liquid methanol and liquefied dimethyl ether.

[0008] In addition, in the liquid fuel production method disclosed in the present application, a dehydration step is carried out to produce dimethyl ether by dehydrating methanol, and the liquefaction step is carried out by pressurizing the dimethyl ether produced in the dehydration step.

[0009] In addition, in the method for producing liquid fuel disclosed herein, the liquefaction step is a step of liquefying dimethyl ether by applying a pressure of 1 MPa or more, and the mixing step is a step of mixing liquid methanol pressurized to 1 MPa or more and dimethyl ether pressurized to 1 MPa or more.

[0010] In the method for producing a liquid fuel disclosed in the present application, the mixing ratio of methanol and dimethyl ether in the mixing step is 8:2 to 2:8 by mass.

[0011] In addition, in the method for producing liquid fuel disclosed herein, the liquefaction step is carried out in a liquefaction device that pressurizes and liquefies liquid dimethyl ether, and the liquefaction device is characterized by having a discharge part that discharges the liquid dimethyl ether from a lower part.

[0012] Furthermore, the liquid fuel disclosed in the present application is characterized by being a mixture of liquid methanol and dimethyl ether liquefied under pressure.

[0013] The liquid fuel manufacturing method and liquid fuel disclosed herein have excellent effects such as being able to improve ignition performance while reducing the environmental load.

[0014] FIG. 1 is an explanatory diagram conceptually illustrating a method for producing a liquid fuel disclosed herein; FIG. 2 is a graph showing the saturated vapor pressure of DME used in the liquid fuel disclosed herein; FIG. 3 is a process diagram generally illustrating an example of a system for realizing the method for producing a liquid fuel disclosed herein; FIG. 4 is a schematic diagram conceptually illustrating an injection model using the liquid fuel disclosed herein; FIG. 5 is an experimental example showing the change over time in the spray of the liquid fuel disclosed herein, compared with liquid methanol fuel; FIG. 6 is an experimental example showing the change over time in the state of a spray flame of the liquid fuel disclosed herein, compared with liquid methanol fuel and diesel; FIG. 7 is a graph of an experimental example showing the change over time in the heat release rate of the liquid fuel disclosed herein, compared with liquid methanol fuel and diesel; FIG. 8 is a graph of an experimental example showing the relationship between the temperature and ignition delay of the liquid fuel disclosed herein, compared with liquid methanol fuel and diesel; FIG. 9 is an experimental example showing the luminance distribution of the light emission state of a spray flame of the liquid fuel disclosed herein, compared with liquid methanol fuel and diesel;

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes in detail preferred embodiments of the present invention. Note that the following preferred embodiments are merely examples of the present invention and are not intended to limit the technical scope of the present invention.

[0016] <Application Examples> The liquid fuel disclosed herein is used as fuel for various systems, such as fuel for mobile bodies such as ships, cars, and aircraft, and fuel for stationary power sources such as pumps and generators. Below, a method for producing the liquid fuel disclosed herein will be described with reference to the drawings.

[0017] FIG. 1 is an explanatory diagram conceptually illustrating a method for producing a liquid fuel disclosed herein. The method for producing a liquid fuel disclosed herein uses methanol as a raw material. In the production method disclosed herein, a dehydration step is carried out in which methanol is dehydrated to produce dimethyl ether (hereinafter referred to as DME). The dehydration reaction in the dehydration step is shown in the following formula (1). In the dehydration step, methanol is separated into DME and water. After the dehydration step, it is preferable to remove the water, but it is not necessary to remove it completely.

[0018] 2CH 3 OH → CH 3 OCH 3 + H 2 O...Formula (1)

[0019] Next, a liquefaction step is carried out in which the obtained DME is liquefied by pressurization. FIG. 2 is a graph showing the saturated vapor pressure of DME used in the liquid fuel disclosed herein. FIG. 2 shows the relationship between the temperature and saturated vapor pressure of DME, with temperature on the horizontal axis and saturated vapor pressure on the vertical axis. DME is a gas at room temperature and atmospheric pressure, but becomes liquid when pressurized. The pressure in the liquefaction step is preferably 1 MPa or higher, and more preferably 2 MPa or higher. The liquefied DME can maintain its liquid state even if the temperature rises to about 320 K as long as the pressure is 1 MPa or higher, but it is preferable to control the pressure at 8 MPa or higher.

[0020] On the other hand, a pressurizing step is carried out to pressurize methanol. The pressurization of methanol is a pretreatment for mixing with DME, and is carried out as a process of pressurizing methanol to a pressure corresponding to the pressure of DME, for example, 1 MPa, so that the methanol can be mixed at a pressure approximately equal to that of DME during mixing.

[0021] Next, a mixing process is carried out in which liquid methanol and liquefied DME are mixed. The methanol and DME are mixed under approximately the same pressure, for example, 1 MPa. In the mixing process, liquid methanol and DME are mixed to produce a liquid fuel. The mixture ratio of methanol and DME is, for example, 7:3 by mass. A mixture ratio of methanol and DME of approximately 8:2 to 2:8 ensures sufficient functionality as a liquid fuel. Note that the mixture ratio of methanol and DME in the liquid fuel is designed and controlled depending on the state and required characteristics of the engine to be used, and is therefore preferably 5:5 to 7:3 by mass.

[0022] DME liquefied by pressure and liquid methanol pressurized to the same pressure have a high affinity, making it possible to obtain a homogeneous liquid fuel.

[0023] Next, an example of a system for realizing the liquid fuel production method disclosed herein will be described. FIG. 3 is a process diagram that schematically illustrates an example of a system for realizing the liquid fuel production method disclosed herein. The system illustrated in the process diagram of FIG. 3 includes various components such as a fuel tank 1, a vaporizer 2, a denaturing device 3, a liquefaction device 4, a mixing tank 5, and a pressurizing device 6. The fuel tank 1 is a liquid tank that stores liquid methanol as fuel. The vaporizer 2 is a device that vaporizes methanol supplied from the fuel tank 1. The denaturing device 3 is a device that dehydrates gaseous methanol supplied from the vaporizer 2 to produce gaseous DME. The liquefaction device 4 is a pressure-resistant device that pressurizes gaseous DME supplied from the denaturing device 3 to produce liquid DME. The mixing tank 5 is a device that mixes liquids, and pressurizes methanol supplied from the fuel tank 1 and mixes it with liquid DME supplied from the liquefaction device 4. The pressurizing device 6 is a device such as a high-pressure cylinder in which gaseous nitrogen is stored, and supplies the stored nitrogen as high-pressure gas to the liquefaction device 4 and the mixing tank 5, thereby pressurizing the liquefaction device 4, the mixing tank 5, and the inside of the piping. The liquid fuel mixed under high pressure in the mixing tank 5 is transferred from the mixing tank 5 to the fuel spray system, which is the next process. These various tanks and devices are connected by piping such as the example shown in Figure 3, and each piping is provided with various devices such as valves, pressure gauges, and pressure reducing valves.

[0024] The liquefaction device 4 is connected to its top with a pipe for supplying gaseous DME from the modification device 3 and a pipe for supplying nitrogen from the liquefaction device 4. The bottom (lower part) is formed with a discharge section 40 for discharging pressurized liquid DME to the mixer 4, and a pipe is connected to the discharge section 40. The liquefaction device 4 receives gaseous DME and nitrogen from its top and discharges liquid DME from its bottom, enabling stable discharge of liquid DME even when the interior is in a gas-liquid mixed state. Furthermore, by supplying nitrogen into the liquefaction device 4 to increase the pressure, re-vaporization of liquefied DME can be suppressed. Since liquefied DME may vaporize within the piping, the piping can also be pressurized to suppress vaporization of DME during transfer. When the liquefaction device 4 is configured using a replaceable high-pressure cylinder appropriately disposed within the system, the liquefaction device 4 is positioned so that the outlet of the high-pressure cylinder is located downward as the discharge section 40.

[0025] The piping for supplying DME discharged from the discharge port 40 to the mixing tank 5 extends to near the inner bottom of the mixing tank 5, and discharges DME from near the inner bottom of the mixing tank 5. The piping for supplying DME is also used to discharge the liquid fuel mixed in the mixing tank 5 and transfer it to a fuel spray system. Since the piping for supplying DME extends to near the inner bottom of the mixing tank 5, when DME is supplied to the mixing tank 5 storing methanol, it is possible to supply DME by discharging nitrogen above the methanol and reducing the pressure. Note that the mixing tank 5 may have openings at its bottom that serve as a supply port and a discharge port, and pipes for supplying DME and discharging the mixed fuel may be attached to the openings. By attaching the piping to the bottom of the mixing tank 5, in addition to the supply of DME by discharging nitrogen, the mixed liquid fuel can be easily discharged without leaving any liquid fuel in the tank.

[0026] FIG. 4 is a schematic diagram conceptually illustrating an injection model using a liquid fuel disclosed herein. The injection model illustrated in FIG. 4 is a model of a portion of a fuel spray system to which liquid fuel is supplied from the system illustrated in FIG. 3. FIG. 4 is a schematic diagram illustrating a state in which liquid fuel is injected from an injection nozzle on the top surface into a rectangular box that represents an engine combustion chamber. The liquid fuel disclosed herein, produced by mixing liquid methanol and DME, is injected into the combustion chamber from the injection nozzle. Because DME is mixed with methanol in liquid form, an engine using the liquid fuel disclosed herein does not require separate fuel supply of methanol and DME. In particular, it is possible to design an engine without constructing a complex fuel supply system that would be required when using, for example, liquid methanol and gaseous DME.

[0027] In the injection model shown in Figure 4, the injected liquid fuel is injected in the injection direction and also spreads in the width direction relative to the injection direction. The reach of the injection in the injection direction and the spread in the width direction need to be designed appropriately depending on the size and shape of the combustion chamber. The liquid fuel disclosed in the present application has a higher straightness the higher the mixture ratio of methanol, and a higher mixture ratio of DME, so it is possible to control the injection state by the mixture ratio.

[0028] Next, we present the results of several experiments comparing the combustion characteristics of the liquid fuel disclosed herein with liquid methanol fuel and diesel. In the following experiments, the liquid fuel disclosed herein (hereinafter referred to as the blended fuel) was a blended fuel prepared with a molar fraction ratio of DME:methanol = 0.37:0.63. Figure 5 shows an example experiment comparing the time course of the spray of the liquid fuel (blended fuel) disclosed herein with that of liquid methanol fuel. The upper part of Figure 5 shows an example experiment of the injection of the blended fuel, and the lower part of Figure 5 shows an example experiment of the spray using liquid methanol fuel for comparison. The spray is plotted horizontally, showing time changes every 0.02 ms from the start of injection. The vertical axis represents the distance from the tip of the injection nozzle in mm. The injection nozzle had an orifice diameter of 0.125 mm, an injection pressure of 40 MPa, an ambient pressure of 0.1 MPa, and an injection command period of 0.800 ms. From the comparative experiment illustrated in FIG. 5, it can be confirmed that the mixed fuel causes reduced pressure boiling and the spray spreads more than the liquid methanol fuel.

[0029] FIG. 6 is an experimental example showing the change over time in the spray flame condition of the liquid fuel (blended fuel) disclosed herein, compared with liquid methanol fuel and diesel. The upper row of FIG. 6 shows the experimental results for the blended fuel, while the middle and lower rows show liquid methanol fuel and diesel for comparison. The experimental example shown in FIG. 6 shows photographs showing the spray flame condition when fuel is injected at an ambient temperature of 780 K, arranged horizontally as time changes every 0.5 ms from the start of injection. The vertical axis indicates the distance from the injection nozzle tip in mm. From the experimental example shown in FIG. 6, it can be seen that the brightness of the spray flame light is higher for diesel fuel and lower for the blended fuel and liquid methanol fuel. This indicates that the blended fuel and liquid methanol fuel generate less soot than diesel.

[0030] FIG. 7 is a graph of an experimental example showing the change over time in the heat release rate of the liquid fuel (blended fuel) disclosed herein compared with liquid methanol fuel and diesel. In FIG. 7, the horizontal axis represents the elapsed time from the start of injection in ms, and the vertical axis represents the heat release rate in J / ms, showing the relationship between them. In the graph, the experimental results for the blended fuel are shown by a solid line, those for liquid methanol fuel by a dashed line, and those for diesel by a dashed-dotted line. FIG. 7 shows the change over time in the heat release rate during the experiment shown in FIG. 6. In FIG. 7, the rise in the heat release rate indicates the ignition timing, and the differences between the fuels can be seen.

[0031] FIG. 8 is a graph of an experimental example showing the relationship between the temperature of the liquid fuel (mixed fuel) disclosed herein and ignition delay, compared with liquid methanol fuel and diesel fuel. FIG. 8 shows the relationship between ambient temperature on the horizontal axis and ignition delay on the vertical axis. In the graph, the experimental results for the mixed fuel are shown with a solid line and a symbol "□," liquid methanol fuel is shown with a dashed line and a symbol "◇," and diesel fuel is shown with a dashed line and a symbol "△." The experimental example shown in FIG. 8 confirms that the ignition delay for the mixed fuel tends to increase as the ambient temperature decreases, but the degree of this increase is smaller than that for methanol, and the behavior is closer to that of diesel fuel. Note that methanol no longer ignites at ambient temperatures below 780 K.

[0032] Figure 9 is an experimental example showing the luminance distribution of the light emission state of the spray flame of the liquid fuel (blended fuel) disclosed herein, compared with liquid methanol fuel and diesel. Figure 9 shows the luminance distribution of the spray flame of the liquid fuel (blended fuel) disclosed herein, in this order from left to right: blended fuel, liquid methanol fuel, and diesel. The vertical axis indicates the distance from the tip of the injection nozzle in mm. The photograph shown in Figure 9 shows the light emission state when the ambient temperature is 900 K, at which the difference in ignition delay due to the fuel can be ignored. Furthermore, because diesel has a high luminance flame, the exposure time during photography was shortened and a 3.1% ND filter was used to suppress the luminance.

[0033] FIG. 10 is a graph of an experimental example showing the luminance distribution of the light emission state of the spray flame of the liquid fuel (blended fuel) disclosed herein compared with liquid methanol fuel and diesel fuel. FIG. 10 shows the relationship between the radial distance from the injection nozzle orifice center in mm on the horizontal axis and the luminance on the vertical axis. Note that the luminance on the vertical axis is a normalized value with the maximum luminance set to 1. In the figure, the blended fuel is shown by a solid line, the liquid methanol fuel by a dashed line, and the diesel fuel by a dashed-dotted line. FIG. 10 shows the luminance distribution at a distance of 50 mm from the injection nozzle in the experiment shown in FIG. 9. It can be seen from FIGS. 9 and 10 that the diesel fuel spray flame has strong luminance at the outer edge, whereas the blended fuel and liquid methanol fuel have strong luminance near the spray center axis.

[0034] The liquid fuel disclosed herein, obtained by blending the liquid methanol and DME produced as described above, offers excellent advantages, such as suppressing the generation of environmentally harmful substances such as soot during combustion, compared to fuels produced from fossil fuels such as heavy oil and light oil. Furthermore, because the liquid fuel disclosed herein is produced from methanol using carbon dioxide as a raw material, it is a promising fuel that is in line with industrial policies aimed at achieving carbon neutrality. Furthermore, the liquid fuel disclosed herein uses methanol, which has a low environmental impact, while containing DME, which has a low ignition point, making it easy to ignite and suitable for engines such as diesel engines. Furthermore, the liquid fuel disclosed herein offers excellent advantages, such as eliminating the need for a complex fuel supply system when supplied to the combustion chamber of an engine. Furthermore, the liquid fuel disclosed herein offers excellent advantages, such as the ability to control the injection state into the combustion chamber by adjusting the mixture ratio of methanol and DME.

[0035] The present invention is not limited to the above-described embodiments, but can be embodied in various other forms. Therefore, these embodiments are merely illustrative in all respects and should not be interpreted as limiting. The scope of the present invention is defined by the claims and is not limited in any way by the text of the specification. Furthermore, all modifications and variations within the equivalent range of the claims are within the technical scope of the present invention.

[0036] For example, the mixture ratio of the liquid fuel disclosed herein is not limited to the above-mentioned values ​​and can be various mixture ratios. As a specific example, the mixture ratio of methanol and DME in the liquid fuel disclosed herein can be selected arbitrarily, taking into consideration combustion efficiency, heat generation state, fuel consumption, remaining fuel material, and operation schedule. This mixture ratio can be expressed as a mass ratio or a volume ratio. For example, the mixture ratio of methanol and DME can be set to a specific mass ratio or volume ratio, such as 99:1, 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, 65:35, 60:40, 55:45, 50:50, 45:55, 40:60, 35:65, 30:70, 25:75, 20:80, 15:85, 10:90, or 5:95. Furthermore, these mass ratio or volume ratio values ​​can be set as upper or lower limits of a design range depending on the required characteristics, and may be set to specific ranges such as 10:90 to 90:10, 20:80 to 80:20, 30:70 to 70:30, 40:60 to 60:40, 50:50 to 60:40, 60:40 to 70:30, etc. As described above, the mixture ratio of the liquid fuel disclosed herein can be designed as appropriate.

[0037] Furthermore, the liquid fuel production method disclosed herein can also be controlled to change the mixture ratio of the liquid fuel being produced in real time during use as fuel, depending on conditions such as heat generation, fuel consumption, remaining fuel material, and driving operation. For example, the liquid fuel production method disclosed herein can be controlled to increase the DME ratio at the start of operation to improve ignition performance, and then increase the methanol ratio once operation reaches a steady state. Furthermore, the liquid fuel production method disclosed herein can be controlled to efficiently use the fuel by setting the mixture ratio of methanol to DME in the range of 10:90 to 50:50 at the start of operation, and then setting the mixture ratio of methanol to DME to 50:50 to 90:10 thereafter. Furthermore, the liquid fuel production method disclosed herein can set a control range for the mixture ratio, rather than keeping it constant, and vary the mixture ratio within that range depending on conditions.

[0038] The liquid fuel production method disclosed herein can be linked to various systems that use the produced liquid fuel. For example, the liquid fuel production method disclosed herein can be applied to an assembly of a liquid fuel production unit to which the method is applied, an energy conversion unit that combusts the liquid fuel produced in the liquid fuel production unit to convert it into mechanical energy, and an execution unit that performs physical work by using the mechanical energy obtained by the conversion in the energy conversion unit. The liquid fuel production unit is a unit to which the liquid fuel production method disclosed herein is applied. The energy conversion unit is a unit that combusts the liquid fuel disclosed herein to convert it into mechanical energy, and is realized as a mechanism such as an engine such as a diesel engine, a boiler section of a boiler, or a combustion-type generator. The execution unit is a unit that performs physical work by using the mechanical energy generated by the liquid fuel disclosed herein, and is realized as a mechanism such as a power plant connected to an engine such as a diesel engine, a steam generation section of a boiler, or a power generation section of a combustion-type generator. A system including these units may be separate devices, or may be composed of a device in which one or more units are integrated. The liquid fuel production method disclosed herein achieves efficient energy supply to a platform in which such a system is used. Examples of such platforms include, but are not limited to, moving objects such as ships, railway vehicles, automobiles, and aircraft, as well as various facilities and structures that require energy consumption, such as ordinary houses, power plants, boiler facilities, chemical manufacturing processes, farms, and university campuses.

[0039] REFERENCE SIGNS LIST 1 fuel tank 2 vaporizer 3 denaturing device 4 liquefying device 40 discharge section 5 mixing tank 6 pressurizing device

Claims

1. a liquefaction step of liquefying dimethyl ether by applying a pressure of more than 3 MPa; a mixing step of mixing liquid methanol pressurized to more than 3 MPa and the liquefied dimethyl ether in a mass ratio of 5:5 to 7:3; A method for producing liquid fuel, comprising:

2. 2. The method for producing a liquid fuel according to claim 1, a dehydration step of dehydrating methanol to produce dimethyl ether; The liquefaction step is carried out by pressurizing the dimethyl ether produced in the dehydration step to 8 MPa or more, and the mixing step is carried out by pressurizing the dimethyl ether produced in the dehydration step to 8 MPa or more. A method for producing liquid fuel, comprising:

3. (delete)

4. (delete)

5. 3. The method for producing a liquid fuel according to claim 1 or 2, The liquefaction step comprises: This is carried out in a liquefaction device that pressurizes and liquefies liquid dimethyl ether, The liquefaction device comprises: It has a discharge part that discharges liquid dimethyl ether from the bottom. A method for producing liquid fuel, comprising: