RU2779031C2 - Internal combustion engine as chemical reactor for production of synthesis gas from hydrocarbon raw materials - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the creation of synthesis gas from hydrocarbon flows. An internal combustion engine operates in fuel-rich conditions by means of adjustment of one or more operating parameters, such as, for example, a throttle valve, an ignition moment, a load attached to the engine, fuel pressure, supercharger power, and preheater power, in order to maintain the specified engine speed and a waste gas temperature. Engine operation in such conditions provides for a possibility for the engine of functioning as a reforming installation creating synthesis gas containing hydrogen and carbon monoxide.

EFFECT: use of an internal combustion engine as a synthetic gas generator.

35 cl, 9 dwg, 1 tbl

Description

Related Applications

[0001] This application claims benefit from U.S. Provisional Patent Application Serial Number 62/565,844, filed September 29, 2017, entitled "INTERNAL COMBUSTION ENGINE AS A CHEMICAL REACTOR TO PRODUCE SYNTHESIS GAS FROM HYDROCARBON FEEDS", the contents of which are incorporated herein by reference in in all its fullness.

Federally funded research or development

[0002] This invention was made with government support under Grant No. DE-AR0000506 issued by the US Department of Energy. The government has some rights in the invention.

Technical field

[0003] The present invention generally relates to the generation of synthesis gas, in particular using an internal combustion engine as a synthesis gas generator.

State of the art

[0004] A variety of processes and activities create gaseous volatile hydrocarbon streams. Often these gaseous streams exist at low pressure and may additionally contain a variety of contaminants. Consequently, the gaseous streams may have little intrinsic value, and the costs of removing contaminants and compressing the gas (eg, to increase pressure to allow natural gas to be introduced into the main pipeline) may be prohibitively expensive. With these limitations, gaseous streams are often eliminated by flaring, calcining or blowing.

[0005] Recently, there has been increased interest in making more productive use of these low quality hydrocarbon streams. One such area is the use of a hydrocarbon stream as a feed gas in the production of synthesis gas (syngas). Syngas can be created from the partial combustion of organic raw materials (volatile hydrocarbons, coal, petcoke, biomass, oil) and is primarily composed of hydrogen (H ₂ ) and carbon monoxide (CO). Syngas often contains contaminants (including H ₂ S, COS) depending on the starting feedstock. Many syngas production processes use catalytic reformers to partially oxidize organic feedstocks. Although catalysts are useful in increasing the reaction rate and reducing the reaction temperature, many catalysts are made from expensive materials, are susceptible to poisoning from sulfur compounds present in the gas stream, and fouling from soot and other particles.

[0006] Synthetic gas is the starting material for the production of many chemicals. Syngas can also be used to generate power in a gas turbine or engine-based generator. Syngas can also be used to create H ₂ by converting CO and water vapor into H ₂ and carbon dioxide (CO ₂ ) through the Water Gas Shift (WGS) process. The ratio of H ₂ to CO of the process gas typically needs to be carefully adjusted to meet the needs of downstream applications.

[0007] Recently, US Pat. No. 9,169,773 (Bromberg et al.) has described a liquid fuel production system with a reformer using an engine to generate a hydrogen-rich gas. The systems described operate with an air/fuel ratio, fuel ratio, 2.5 < φ < 4.0. They also describe that homogeneous fuel compression ignition (HCCI), partial premix compression ignition (PCI), or reaction controlled compression ignition (RCCI) can be used for an efficient engine-based reformer. They report that "In the resultant burner flame, as well as in cylinder calculations, lower ratios result in higher conversion energy, higher peak in cylinder temperatures, lower selectivity towards hydrogen and CO…"

[0008] US Patent No. 2,391,687 (Eastman et al.) describes an engine for generating syngas that runs on 90% or more pure O ₂ and has a ratio of 2.8-4.0.

The essence of the invention

[0009] In order to overcome the aforementioned problems, in whole or in part, and/or other problems that may be observed by those skilled in the art, the present invention provides the methods, processes, systems, equipment, tools, and/or devices that are described by way of example in implementations below.

[0010] According to one embodiment, a method for operating an internal combustion engine under fuel rich conditions includes: starting the engine with a supply gas having an initial air-fuel ratio; incrementally increasing the air-fuel ratio to form a fuel-rich feed gas; and while increasing the air/fuel ratio, adjusting one or more of the throttle valve, ignition timing, engine load, fuel pressure, power for the blower acting on the feed gas, and power for the preheater acting on the feed gas to maintain an air-fuel ratio of about 1.6-2.4. In an embodiment, an engine speed between about 1000-2000 revolutions per minute (rpm) and an exhaust gas temperature of less than about 900°C are maintained.

[0011] According to another embodiment, a method of operating an internal combustion engine under fuel rich conditions includes: maintaining an initial set of conditions after engine start for exhaust gas backpressure, intake manifold pressure, engine speed, ignition timing, air-fuel ratio in fuel gas and fuel gas inlet temperature; increasing the fuel gas inlet temperature while maintaining the fuel gas air-fuel ratio, and monitoring the methane and oxygen content of the engine exhaust gas; and adjusting ignition timing in response to observed methane and oxygen levels.

[0012] According to another embodiment, the gas reformer system is configured to perform any of the methods described herein.

[0013] According to another embodiment, the gas reformer system includes: an internal combustion engine comprising a fuel gas inlet, an exhaust gas outlet, a plurality of cylinders, an ignition control system, a throttle valve, a fuel gas preheater, and a supercharger , wherein the internal combustion engine is configured to operate with an air-fuel ratio of the fuel gas between approximately 1.6 and 2.4.

[0014] Other devices, equipment, systems, methods, features and advantages of the invention will or will become apparent to a person skilled in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included in this specification, be within the scope of the present invention, and be protected by the accompanying claims.

Brief description of the drawings

[0015] The invention may be better understood by reference to the following drawings. The components in the drawings are not necessarily drawn to scale, with emphasis instead being placed on illustrating the principles of the invention. In the drawings, like reference numerals designate corresponding parts throughout the various views.

[0016] FIG. 1 is a schematic cross-sectional view of an exemplary internal combustion engine cylinder according to some embodiments.

[0017] FIG. 2 is a schematic view of a system for producing synthesis gas with an internal combustion engine, in accordance with some embodiments.

[0018] FIG. 3 is a schematic view of a system for producing synthesis gas with an internal combustion engine, in accordance with some embodiments.

[0019] FIG. 4 is a schematic view of a system for producing synthesis gas with an internal combustion engine, in accordance with some embodiments.

[0020] FIG. 5 is an exemplary flowchart of a method for starting an engine under fuel rich conditions, in accordance with some embodiments.

[0021] FIG. 6 is an exemplary flowchart of a method for operating an engine under fuel rich conditions, in accordance with some embodiments.

[0022] FIG. 7 is a plot of fuel-intake air temperature for various air-fuel ratios according to some embodiments.

[0023] FIG. 8 is a graph of H ₂ to CO ratios for various air-fuel ratios according to some embodiments.

[0024] FIG. 9 is a graph of natural gas conversion rates for various air-fuel ratios, in some embodiments.

Detailed description of the invention

[0025] As used herein, the term "syngas" refers to synthesis gas. In the context of the present description, syngas is a mixture of at least carbon monoxide (CO) and diatomic hydrogen gas (H ₂ ). Depending on the embodiment, the syngas may further include other components such as, for example, water, air, diatomic nitrogen gas (N ₂ ), diatomic oxygen gas (O ₂ ), carbon dioxide (CO ₂ ), sulfur compounds ( e.g. hydrogen sulfide (H ₂ S), carbon sulphide (COS), sulfur oxides (SO _x ), etc.), nitrogen compounds (e.g. nitrogen oxides (NO _x ), etc.), carbonyls metals, hydrocarbons (e.g. CH ₄ )), ammonia (NH ₃ ), chlorides (e.g. hydrogen chloride (HCl)), hydrogen cyanide (HCN), rare metals and metalloids (e.g. mercury (Hg), arsenic (As) , selenium (Se), cadmium (Cd), etc.) and their compounds, particulate matter (PM), etc.

[0026] As used herein, the term "lower hydrocarbon" refers to low molecular weight hydrocarbons including, but not limited to, methane, ethane, propane, and butane.

[0027] As used herein, the term "load" may mean an electrical heater, dynamometer, water bath, etc. By increasing or decreasing the load, the motor can run at a constant speed when the input conditions change. You can also vary the load to change engine temperature or output ratios.

[0028] When used herein, the term "natural gas" refers to a mixture of hydrocarbon (HC) gases, consisting mainly of methane and smaller amounts of higher alkanes. Depending on the embodiment, natural gas may further include non-HC species such as one or more of those noted above, as well as carbon disulfide (CS ₂ ) and/or other disulfides, and mercaptans (thiols) such as methanethiol (CH ₃ SH) and ethanethiol (C ₂ H ₅ SH), and thiophenes such as thiophene (C ₄ H ₄ S) and other organosulfur compounds.

[0029] The present invention provides methods for using an internal combustion engine as a syngas generator. Additionally, the process can be used in conjunction with methanol production, as well as other chemical production processes. The described methods can use a wide variety of hydrocarbon sources scattered throughout the world. For example, oil and natural gas production wells are located in many remote areas of the US, and each individual mine, compressor, pneumatic device, and storage tank in the mine can produce a hydrocarbon release stream. Due to the small volume, low pressure, and potential contamination of these hydrocarbon streams, they are often flared or purged. Compressing and treating these disparate streams for collection into a natural gas pipeline can be prohibitively expensive. The methods of the present invention can use mass-produced internal combustion engines operating under specific conditions to partially oxidize these hydrocarbons and produce syngas that can be of higher value and make syngas collection economically viable.

[0030] Internal combustion engines have been developed and used for decades to produce power, typically either to propel vehicles, drive mechanical devices, or generate electricity. In each of these uses, the focus has been on efficient and complete combustion of the fuel in order to maximize the power generated. Internal combustion engines, however, have characteristics that are of interest for other applications. Features such as heat management from the coolant and radiator system to control engine temperature, the ability to generate high cylinder pressures, the function of short cylinder residence times, and valve pressure control can all be used in chemical conversion processes when the engine will serve as chemical reactor. In this application, the focus is on controlling engine parameters to maximize the desired chemical conversion as opposed to energy generation. In some cases, a chemical reaction can create energy. Alternatively, energy can be added by external rotation of the shaft in other cases. Any chemical reaction that operates on a short residence time and takes advantage of the characteristics listed above can potentially be applied to use the engine as a chemical reactor. Here we describe one such application for converting volatile hydrocarbons into syngas.

[0031] FIG. 1 illustrates a schematic cross-sectional view of one cylinder 105 of an internal combustion engine 100 according to various embodiments. Engine 100 may further comprise a combustion chamber 110 in cylinder 105. Piston 115 may be located in cylinder 105 and move up and down in cylinder 105 thereby defining a variable volume of combustion chamber 110. Combustion chamber 110 is at its minimum volume when piston 115 is at its highest position in cylinder 105 (referred to as top dead center (TDC)), and at its maximum volume when piston 115 is at its lowest position in cylinder 105 (referred to as bottom dead center). dead center (BDC)). Piston 115 may be coupled to crankshaft 120 by connecting rod 125. Engine 100 may further include a head 130 coupled to the top of cylinders 105. Head 130 may receive one or more intake valves 135 and one or more exhaust valves 140. Each intake valve 135 may serve to open or close inlet 145, while each outlet valve 140 may serve to open or close outlet 150. Inlet 145 may be in fluid communication with combustion chamber 110 to allow a mixture of fuel and oxidizer (called charge) to flow into the combustion chamber 110. The outlet 150 may also be in fluid communication with the combustion chamber 110 to allow gases to flow out of the combustion chamber 110. Head 130 may also include one or more spark plugs 155 that may extend at least partially into combustion chamber 110 and provide an ignition source for charging.

[0032] Although not shown in FIG. 1, engine 100 may further comprise a preheater to increase the temperature of one or both of the fuel and oxidizer before entering intake port 145, and a supercharger to pressurize one or both of the fuel and oxidizer before entering intake port 145. The preheater may comprise a heat exchanger to extract some of the heat, such as exhaust gases from engine 100. Alternatively, the preheater may obtain thermal energy through other processes known in the art, such as electrically powered heaters, combustion of a secondary fuel, or exhaust gas scavenging heat from another process. The supercharger may include a turbine to extract energy from the exhaust gases from the engine 100. Alternatively, the supercharger may be powered by other processes known in the art, such as an electric motor or exhaust gas scavenging power from another process.

[0033] In some non-limiting embodiments, the implementation of the engine 100 can be adapted to operate using a 4-stroke process. The 4-stroke process may start with piston 115 at TDC, for example, and then it starts moving down. Inlet valve 135 moves downward, thereby placing inlet 145 in fluid communication with combustion chamber 110. The piston 115 moves downward, allowing the charge to flow into the combustion chamber 110. When piston 115 reaches BDC, intake valve 135 closes. Piston 115 then moves upward, compressing the charge. As piston 115 approaches TDC, spark plug 155 generates a spark that ignites the charge. In various embodiments, as discussed further below, a spark may be generated before piston 115 reaches TDC. As the charge burns, the pressure in combustion chamber 110 increases and pushes piston 115 down. When the piston 115 reaches the BDC, the exhaust valve 140 moves downward, thereby placing the exhaust port 150 in fluid communication with the combustion chamber 110. As piston 115 moves towards TDC, combustion gases from the burnt charge are expelled from exhaust port 150. When piston 115 reaches TDC, exhaust valve 140 closes and the cycle repeats.

[0034] Although the specifics of each process are not described herein, the engine 100 in various embodiments may be configured to operate according to a 2-stroke process, a 5-stroke process, a 6-stroke process, a compression ignition process (e.g., diesel) , jet engine, turbine, rotary engine, or any other type of engine known in the art. The present invention focuses on the 4-stroke process due to its ubiquity and continued availability, but limitation on the scope of the invention should not be implied.

[0035] Typically, hydrocarbons and oxygen are the fuel and oxidant, respectively, combusted in engine 100. The general stoichiometric chemical equation for burning hydrocarbon in oxygen is provided by Equation 1:

Thus, for stoichiometric complete combustion, all of the hydrocarbon and oxygen react to form carbon dioxide and water. Thus, for stoichiometric complete combustion, some ratio of fuel to air is required. One indication of how the actual air-fuel ratio compares to the stoichiometric air-fuel ratio is the mixture ratio (denoted as ɸ). The mixture ratio is calculated by dividing the actual air-fuel ratio by the stoichiometric air-fuel ratio. Mixture ratio values greater than 1 indicate fuel-rich conditions.

[0036] Engine 100 operating according to stoichiometric complete combustion typically operates to extract useful work and heat. However, various embodiments may include operating engine 100 under non-stoichiometric conditions in order to use engine 100 as a chemical reactor. Some embodiments may use fuel-rich conditions (ie, less than the stoichiometric amount of oxygen to burn all of the hydrocarbon) to partially oxidize the hydrocarbon. Without intending to be limited to a particular mechanism of action, under some conditions, engine 100 may operate as a reformer to produce synthesis gas (syngas) containing hydrogen (H ₂ ) and carbon monoxide (CO) according to the chemical reaction provided by Equation 2 :

If the hydrocarbon is methane (CH ₄ ), then the partial oxidation reaction is provided by Equation 3:

Additionally, other reactions seem likely to take place, as well as complete combustion (Equation 1), reforming reactions such as Equations 4 and 5 (shown for methane), and other such known reforming and combustion reactions.

[0037] FIG. 2 is a schematic diagram of a process 200 according to various embodiments in which combustion engine 100 can be used as a chemical reactor to produce, for example, syngas. As discussed earlier, the charge to engine 100 may contain an oxidizer and fuel. The oxidant may comprise air, enriched air, or a gas containing sufficient oxygen. The oxidant may pass through the filter 205 to remove particles and other solid contaminants as well as liquid or gaseous contaminants such as water. The oxidant flow may be controlled by throttle valve 210. Throttle valve 210 may include any flow control device known in the art and may be manually or electronically controlled. The pressure of the oxidizer can be increased by means of the supercharger 215. The supercharger 215 acts as a compressor to increase the pressure, thereby allowing more oxygen to be delivered to each cylinder 105 of the engine 100. The supercharger 215 may be powered by an electric motor, or may otherwise be powered , for example, using residual energy in the exhaust stream of the engine 100 or other process stream. The oxidant may also pass through heater 220 to raise the temperature of the oxidizer before entering engine 100. Heater 220 may use electrically powered heating coils, or a heat exchanger that extracts energy from a process stream, such as the exhaust stream of engine 100 (see, for example, FIG. . four). The fuel may also pass through a filter 225 to remove solid, liquid or gaseous contaminants and through a flow controller 230. The temperature of the fuel stream may be increased by means of a heater 235 operating similarly to the oxidizer heater 220. Mixer 240 may mix oxidizer and fuel in the desired proportion to form a charge delivered to each cylinder 105 of engine 100. Engine 100 may then partially oxidize the charge, as previously described, to create syngas in the exhaust stream. The operation of engine 100 may also generate mechanical energy and heat.

[0038] In various embodiments, process 200 may further comprise a central processing unit (not shown). The CPU may be in communication with and adapted to activate and control one or more individual components of process 200. The CPU may be adapted to store and execute computer code to initiate operation of process 200 in response to observed engine 100 operating conditions and syngas analysis. produced by engine 100. For example, the ratio of H ₂ to CO in the exhaust stream of engine 100 may be observed, and the CPU may adjust one or more individual components of process 200 in response to the observed ratio of H ₂ to CO. Additionally, the CPU may adjust one or more individual components of process 200 in response to observed parameters of engine 100, such as combustion temperature in one or more cylinders 105, intake pressure, exhaust pressure, and the like.

[0039] FIG. 3 is a schematic diagram of a process 300 according to various embodiments in which combustion engine 100 can be used as a chemical reactor to produce, for example, syngas. Fig. 3 illustrates that motor 100 may be connected to a generator 305 to convert mechanical power produced by motor 100 into electrical power. The electrical energy may be used to power the oxidizer heater 220, the gas heater 235, or for any other purpose.

[0040] FIG. 4 is a schematic diagram of a process 400 according to various embodiments in which combustion engine 100 can be used as a chemical reactor to produce, for example, syngas. In process 400, residual heat in the syngas can be used to heat the oxidizer and fuel. The oxidizer heater 220 and the fuel heater 235 may include heat exchangers to transfer heat from the syngas to the oxidizer and fuel streams. The heat exchangers may be of any type known in the art, such as shell and tube, plate tube, and plate fin, and may operate, for example, in a co-current, counter-flow, or cross-flow configuration.

[0041] Engines 100 operating in fuel rich conditions may be susceptible to abnormal combustion known as engine knock or knock. Detonation occurs when the charge bubble ignites outside of the flame front created by the spark and can cause the pressure in cylinder 105 to rise beyond design limits. This increase in pressure has the potential to punch holes in piston 115 or crown 130 leading to catastrophic damage to engine 100.

[0042] Various embodiments comprise methods for starting engine 100 to achieve operation in fuel rich conditions and therefore operate under steady state conditions with no (or minimal) detonation. Fig. 5 illustrates a general flow diagram of various embodiments of a method 500 for starting an engine 100 to achieve operation in fuel rich conditions. Engine 100 may be started with a feed gas having an initial air-fuel ratio at 505. The air-fuel ratio may be incrementally increased at 510 to form a fuel-rich feed gas. At 515, one or more of the following may be adjusted while increasing the air/fuel ratio to maintain engine speed between about 1000-2000 rpm and exhaust gas temperature below about 900°C: throttle valve 210, the ignition timing, the load connected to the engine 100, the fuel pressure, the power for the supercharger 215 acting on the supplied gas, and the power for the preheater 220, 235 acting on the supplied gas.

[0043] Before engine 100 is started, initial operating conditions may be set such that fuel pressure is a value typically lower than ambient pressure, throttle 210 is partially open to a predetermined value, typically less than 50%, ignition timing is set to a first predetermined value, and a load is attached to engine 100. In various embodiments, ignition timing determines when a spark is generated by spark plug 155 and measured relative to the angular position of crankshaft 120 when piston 115 is at TDC. Ignition timing can generally be advanced to generate a spark before piston 115 reaches TDC. The ignition timing advance allows combustion (or the desired amount of partial combustion) of the fuel charge to be completed close to the point where piston 115 reaches TDC. Ignition timing is typically expressed as degrees of rotation of crankshaft 120 before piston 115 reaches TDC, or simply degrees before top dead center (BTDC). In various embodiments, the first predetermined ignition timing may be about 8 degrees BTDC, or about 5 to about 15 degrees BTDC. In other embodiments, the first predetermined ignition timing may be up to about 30 degrees BTDC.

[0044] After engine 100 is initiated to start and engine 100 is allowed to rotate for a short period of time until engine starts, fuel pressure can be increased typically to near ambient pressure to allow engine 100 to operate on its own. Engine speed should be observed after starting. The ignition timing may be gradually advanced up to a second predetermined value while adding load to keep the engine speed between approximately 1000 and 2000 rpm. The second predetermined ignition timing may be approximately 16 degrees BTDC. In other embodiments, the second predetermined ignition timing may range from about 8 degrees to about 28 degrees BTDC, preferably between about 10 and about 20 degrees BTDC.

[0045] As previously discussed, blower 215 may be powered in some embodiments by an electric motor. In such embodiments, supercharger 215 may be initially energized and then power may be incrementally increased while incrementally increasing fuel pressure to maintain engine speed between approximately 1000 and 2000 rpm. In various embodiments, supercharger 215 may be initially energized at an initial predetermined value, typically a setting that delivers air similar to a naturally aspirated engine, and incrementally increased to a second predetermined value in increments that are approximately 10-15%% for a range between these settings. In various embodiments, fuel pressure may be incrementally increased by approximately 0.1 H ₂ O level, although larger increments may be used.

[0046] Throttle 210 may be raised in increments from the initial setting in increments that increase from 1% to 10% until the final throttle position, approximately 90% open, is reached. During throttle 210 increase, fuel pressure may be increased in order to maintain engine speed between approximately 1000 and 2000 rpm. If the performance of the engine 100 drops rapidly during the addition of fuel pressure, then the air/fuel mixture may be too rich. In this situation, the fuel pressure can be reduced and the load is used to control the engine speed. The temperature of the exhaust gas can also be observed and must be maintained at a temperature of less than 900°C by changing one or more of the fuel pressure, throttle 210 and engine load.

[0047] The preheaters 220, 235 may be initially energized such that the preheaters 220, 235 maintain a charge temperature of approximately 200° C. before entering inlet 145. The ignition timing may then be advanced past the BTDC. As is known in the art, the optimum ignition timing and the particular process for retrieving the ignition timing will depend on many factors including, but not limited to, fuel conditions (temperature, pressure, presence of contaminants, etc.), fuel injection timing. , type and condition of the ignition system, engine speed, engine load, and the specific type of engine being used. The power for the blower 215 may be incrementally increased to increase the air supply rate. As the supercharger power increases and as the preheaters 220, 235 heat up, the engine speed can be maintained between approximately 1000 and 2000 rpm by adjusting fuel pressure and load. Once the desired engine performance has been achieved, boosts in supercharger power may be interrupted.

[0048] After the preheaters 220, 235 reach approximately 200°C, the temperature of the preheater may be increased in predetermined increments, typically no more than 15% of the setting, to avoid exceeding the set temperature. As is known in the art, the use of automated control systems can allow larger temperature increments without increasing the risk of overshooting the set temperature. The fuel pressure can be adjusted to keep the engine speed between approximately 1000 and 2000 rpm while the preheater temperature rises. Once the desired air/fuel ratio has been obtained, additional increases in preheater temperature may be interrupted. In various embodiments, the desired air-fuel ratio may be approximately 1.6-2.4.

[0049] If the engine 100 suddenly loses stability during the increase in preheater temperature, the operating temperature in the cylinder 105 may be too high for the current air-fuel ratio at the current manifold pressure. In this situation, power to preheaters 220, 235 may be turned off until stability is restored, and then power to preheaters 220, 235 may be turned back on and preheater temperature and fuel pressure rise may resume.

[0050] While air is often used to supply the oxidizer in the charge, enriched air (eg, up to about 35% by volume O ₂ ) can be used in various embodiments. The use of enriched air can increase engine performance, reduce downstream unit costs, and improve liquid product collection and catalyst activity. Also humidified air or the addition of steam to the feed gas can be used. Increasing the humidity or adding more steam increases the water vapor concentration in the cylinder, allowing a higher hydrogen yield through steam reforming reactions as described in Equation 5 above.

[0051] While methane is used here to describe the predominant fuel, a variety of hydrocarbon fuel mixtures can be used in various embodiments. The operation of the system will in many cases use methane derived from natural gas pipelines, associated gas from oil wells, waste gas streams that would typically be flared, biogas streams, and other such gaseous volatile hydrocarbon streams. Pipeline natural gas is composed primarily of methane, but will have ethane levels between 1-6% and traces of other hydrocarbons, carbon dioxide, nitrogen and other molecules. Similarly, associated gas from oil wells will have high concentrations of ethane and higher hydrocarbons, typically referred to as natural gas condensates such as propane, butane, pentane and hexane. In some cases, NGLs are collected before the remaining natural gas is withdrawn for pipeline, use, or flaring. Syngas engine operation can be run either with this fuel or without removing NGLs by adjusting operating parameters to support conversion and avoid soot formation. Another engine fuel stream may be gas streams from various chemical, manufacturing or industrial processes or storage systems, either as waste or by-products, and such fuels may have a variety of volatile hydrocarbons. When these streams have a sufficiently high fuel concentration (depending on fuel composition) or can be processed to achieve such concentrations, they appear to be potential fuel sources for syngas production to utilize these streams. Additionally, there are many sources of biogas that can be used as fuel for engine-assisted syngas production. For the purposes of the present invention, biogas is defined as a gaseous stream formed from the decomposition of biomass substances containing mainly methane and carbon dioxide, with traces of other components known in the field of biogas. Examples of biogas sources are landfills, animal waste treatment sites and wastewater treatment plants. For biogas applications, pretreatment may be required to remove some carbon dioxide (depending on concentration) from the fuel for efficient engine operation, although complete removal is not required for engine operation. Engine operation is generally insensitive to the presence of carbon dioxide. As described in the composition of natural gas, ethane is typically found in natural gas streams. Other embodiments may use additional ethane either as fuel or mixed with natural gas as fuel. The addition of hydrogen to the fuel stream may also provide benefits in some embodiments with different fuel compositions. This hydrogen may be obtained from external sources or reused from engine operation or downstream processes. One embodiment would either reuse the hydrogen selectively removed from the engine's exhaust gas or reuse a fraction of the engine's exhaust.

[0052] After engine 100 is started to reach fuel rich conditions (such as by implementing, for example, the method described above with reference to FIG. 5), FIG. 6 illustrates another general flow diagram of various embodiments of a method 600 for continuously operating engine 100 under fuel rich conditions. At 605, an initial set of operating conditions may be maintained after engine 100 is started for exhaust gas back pressure, intake manifold pressure, engine speed, ignition timing, fuel gas air/fuel ratio, and fuel gas inlet temperature. The fuel gas inlet temperature may be increased at 610 by increasing the power for the preheater while maintaining the air/fuel ratio. The content of methane and oxygen (assuming methane is a hydrocarbon in the fuel) for the exhaust gas can be observed. The ignition timing may be adjusted at 615 in response to the observed methane and oxygen levels.

[0053] In various embodiments, the initial operating exhaust backpressure may be between approximately atmospheric pressure and 5 bar absolute pressure, the initial operating manifold pressure may be approximately between atmospheric pressure and 2 bar absolute pressure, the initial operating speed of the engine may be approximately between 1000-2000 rpm, the initial operating ignition timing may be approximately between 25-35 degrees BTDC, the initial operating air-fuel ratio may be between approximately 1.6 and 2.4, and the initial fuel gas temperature may be approximately between 200°C and 270°C. Fig. 7 illustrates approximate fuel gas temperature ranges for air-fuel ratios ranging from 1 to 2.

[0054] In various embodiments, adjusting ignition timing in response to observed methane and oxygen comprises observing leakage of methane and oxygen (ie, unreacted methane and oxygen passing through engine 100). If the methane content of the exhaust gas or the oxygen content of the exhaust gas exceed acceptable levels, the ignition timing may be advanced to reduce leakage. The exhaust gas temperature may be observed during the ignition timing advance so that the exhaust gas temperature remains in the range indicated in FIG. 7. In various embodiments, instead of precipitating the ignition timing of all cylinders 105 of engine 100 equally, the ignition timing can be adjusted individually for each cylinder 105 such that the exhaust gas temperature variability of each individual cylinder 105 is in the range of approximately 75°C. .

[0055] Under near-steady state operating conditions of FIG. 8 illustrates the expected ratio of H ₂ to CO in the exhaust gas for a given air-fuel ratio. Thus, engine 100 can be tuned to generate the desired ratio of H ₂ to CO as needed for downstream processes. Fig. 9 illustrates the conversion rate of natural gas as a fuel for engine 100 for a given air-fuel ratio. According to various embodiments, FIG. 8 can be used to determine the air/fuel ratio needed to produce the desired H ₂ to CO ratio, and then FIG. 9 can be used to determine the expected degree of fuel conversion that can occur at a selected air-fuel ratio.

[0056] Example

[0057] The engine system has been configured to create syngas using natural gas coming from a local power company's natural gas pipeline. A commercially available 8-cylinder, 8.8L spark-ignition engine was configured in the system to create high-performance syngas. Air was taken from the environment and a supercharger was used to pressurize the intake manifold to approximately 2 bar. The natural gas was delivered from a utility pipeline meeting the US standard specifications for pipeline natural gas. The typical composition relative to the length of the segments described was 95% v/v methane (CH ₄ ), 4% v/v ethane (C ₂ H ₆ ), 1% v/v carbon dioxide (CO ₂ ) and unmeasured microcomponents. The mixtures of air and natural gas were heated above 200°C before mixing. The mixed feed gas was then fed into the engine cylinders through the intake manifold. By means of spark ignition, the supplied gas was converted to synthetic gas in the cylinder. The engine was operated at 1500 rpm and exhaust gas temperatures were kept below 900°C. The produced syngas was collected via an exhaust manifold and maintained at a pressure between 4-5 bar by downstream pressure control.

[0058] Table 1 shows the syngas composition (average of four passes) from this example with engine 100 operating according to the present invention.

[0059] Table 1 Syngas Composition

Syngas component Volume percentage (dry) _H2 22.3 CO 14.5 _O2 0.15 _CO2 2.9 CH ₄ 1.3 N ₂ 58.9

[0060] The above example is presented for illustrative purposes only and does not limit the invention to the processes used in the example.

[0061] In general, expressions such as “associates” and “in…association with” (e.g., the first component “associates with” or “is in communication with” the second component) are used herein to indicate structural, mechanical , electrical, signal, optical, magnetic, electromagnetic, ionic, or fluid relationship between two or more components or elements. As such, the fact that one component, as mentioned, must communicate with another component is not intended to exclude the possibility that additional components may be present between, and/or operably associate with or engage with, the first and second components.

[0062] It will be understood that various aspects or details of the invention may be changed without departing from the scope of the invention. In addition, the above description is for the purpose of illustration only and not for the purpose of limitation - the invention is defined by the claims.

Claims (41)

1. A method for using an internal combustion engine as a reactor under fuel-rich conditions, comprising the steps of: start the engine using the supplied gas having the original ratio of the components of the air-fuel mixture; incrementally increasing the air-fuel ratio to form a fuel-rich feed gas; and during an increase in the air-fuel ratio, one or more of the throttle valve, ignition timing, load attached to the engine, fuel pressure, power for the supercharger acting on the supplied gas or part of the supplied gas, and power for the preheater acting on the supply gas to maintain an air-fuel ratio of approximately 1.6-2.4. 2. The method of claim 1, wherein the feed gas contains hydrocarbon compounds and an oxygen-containing stream. 3. The method of claim. 1, further comprising the step of setting the initial conditions before starting the engine, at least as one of a predetermined fuel pressure, a partially open throttle, a first predetermined ignition timing value, and a load attached to the engine . 4. The method of claim 3, wherein setting the part throttle comprises setting the throttle to a predetermined setting below 50%. 5. The method of claim 3, wherein setting the first predetermined ignition timing comprises setting the ignition timing to about 5 to about 12 degrees before top dead center (BTDC). 6. The method of claim 1, wherein starting the engine comprises setting the fuel pressure to approximately 0 at the H ₂ O level and allowing the engine to start. 7. The method of claim 1, wherein the engine speed is between about 1000 and 2000 revolutions per minute (rpm) and the exhaust gas temperature is maintained at less than about 900°C. 8. The method of claim 1, wherein the ignition timing adjustment comprises advancing the ignition timing to a second predetermined value while increasing engine load to maintain engine speed between approximately 1000 and 2000 rpm. min. 9. The method of claim 8, wherein the second predetermined ignition timing is between approximately 8 degrees BTDC and approximately 28 degrees BTDC. 10. The method of claim 1, wherein adjusting the power for the blower comprises the step of first supplying power to the blower. 11. The method of claim 10, further comprising increasing power to the supercharger while increasing fuel pressure to maintain engine speed between approximately 1000 and 2000 rpm. 12. The method of claim 1, wherein the throttle adjustment comprises increasing the throttle while increasing fuel pressure and engine load to maintain engine speed between approximately 1000 and 2000 rpm. 13. The method of claim 1, further comprising monitoring the exhaust gas temperature and changing one or more of the fuel pressure, throttle, and engine load to maintain the exhaust gas temperature below about 900°C. 14. The method of claim 1, wherein adjusting the power for the preheater comprises initially energizing the preheater. 15. The method of claim 14, further comprising setting the preheater to its original temperature and pressurizing the fuel as the preheater temperature increases while maintaining the engine speed between about 1000 and 2000 rpm. 16. The method of claim 15 wherein the initial temperature of the preheater is approximately 200°C. 17. The method of claim 1, further comprising adjusting the ignition timing to a third predetermined value. 18. The method of claim 17, wherein the third predetermined ignition timing is between about 20 and about 30 degrees BTDC. 19. The method of claim 11, further comprising increasing power to the supercharger while adjusting fuel pressure and engine load to maintain engine speed between approximately 1000 and 2000 rpm until the desired displacement engine will not be reached. 20. The method of claim 15, further comprising, when the preheater reaches an initial temperature, increasing the temperature of the preheater while adjusting the fuel pressure to maintain the engine speed between approximately 1000 and 2000 rpm until the ratio components of the air-fuel mixture will not reach approximately 1.6-2.4. 21. The method of claim 1 wherein the initial fuel gas air-fuel ratio is approximately 1. 22. A method of operating an internal combustion engine in fuel-rich conditions, comprising the steps of: maintaining an operating set of conditions after engine start for backpressure at the outlet of gases, pressure in the intake manifold, engine speed, ignition timing, fuel gas air-fuel ratio, and fuel gas inlet temperature; increasing the fuel gas inlet temperature while maintaining the fuel gas air-fuel ratio, and monitoring the methane and oxygen content of the engine exhaust gas; and regulate the ignition timing in response to the observed methane and oxygen content. 23. The method of claim 22, wherein the initial operating backpressure at the outlet of the gases is between atmospheric pressure and 5 bar absolute pressure. 24. The method according to claim 22, wherein the operating pressure in the intake manifold is approximately between atmospheric pressure and 2 bar absolute. 25. The method of claim 22, wherein the initial operating speed of the engine is between approximately 1000 and 2000 revolutions per minute (rpm). 26. The method of claim 22, wherein the initial operating ignition timing is between approximately 25 and 35 degrees before top dead center (BTDC). 27. The method of claim 22, wherein the fuel gas air-fuel ratio is approximately 1.6-2.4. 28. The method of claim 22, wherein the initial operating temperature at the fuel gas inlet is between approximately 200°C and 270°C. 29. The method of claim 22, wherein adjusting the ignition timing in response to observed methane and oxygen levels comprises advancing the ignition timing if the observed methane or oxygen levels increase beyond acceptable levels. 30. The method of claim 22, further comprising monitoring the exhaust gas temperature from each engine cylinder. 31. The method of claim 30, further comprising individually adjusting the ignition timing of each cylinder to reduce variability in the exhaust gas temperature of each cylinder in the range of about 75°C. 32. The method of claim 22, wherein the exhaust gas contains a combination of at least two of hydrogen (H ₂ ), carbon monoxide (CO), nitrogen (N ₂ ), steam (H ₂ O), carbon dioxide ( CO ₂ ) and microcomponents. 33. A gas reformer system configured to perform the method of any one of the preceding claims. 34. The gas reformer system of claim 33, wherein the gas reformer system is configured to produce syngas. 35. The gas reformer system of claim 34, wherein the syngas contains hydrogen (H ₂ ) and carbon monoxide (CO).

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