FIELD

[0001 ] The invention is in the field of chemical and mechanical engineering, particularly the use of an internal combustion engine to produce gases containing carbon monoxide and hydrogen from partial oxidation of hydrocarbon fuels.

BACKGROUND

[0002] The term "stranded gas" has been used to refer to hydrocarbon gases that are wasted or unused. Stranded gas in the form of landfill gas or flare gas offers a rich, albeit typically contaminated, pool of methane. For example, landfill gases and other biogases produced in anaerobic digestion generally contain methane along with significant quantities of C0 ₂ , N ₂ and at least some impurities such as H ₂ S and mercaptans. However, these potential resources often do not warrant development of the infrastructure necessary to extract value. As a result, they are mostly combusted and vented to the atmosphere or left untapped - stranded.

[0003] On-site processing of stranded gas to produce high value products, such as liquid fuels or other petrochemicals suited for transportation, may offer an approach to effectively utilize these otherwise wasted resources. Stranded gas can for example be converted to synthesis gas (CO + H ₂ ) via a variety of processes such as steam methane reforming, dry methane reforming, partial oxidation, or autothermal (adiabatic oxidative) reforming. Conventional reactors typically utilize nickel based catalysts for the reforming or partial oxidation process, while some plasma reformers utilize a plasma arc instead of a catalyst bed.

[0004] Steam methane reforming typically leads to a synthesis gas product having a H ₂ :CO ratio of over 3, adiabatic reforming typically generates a synthesis gas product having a H ₂ :CO ratio ranging between 2.3 - 2.7, and partial oxidation of methane generally provides a synthesis gas product having a H ₂ :CO ratio ranging between 1 .8 to 2.1 . In any of these processes, the H ₂ :CO ratio from the outlet of the synthesis gas production unit can be modified by utilizing a water gas shift reactor downstream:

CO + H ₂ 0 <→ C0 ₂ + H ₂ ... (Rxn 1 ) [0005] In a partial oxidation reactor, methane is combusted with a limited supply of oxygen to form a mixture of CO, H ₂ , C0 ₂ and H ₂ 0. The reaction is highly exothermic, and may be used as the combustion cycle of a spark ignition piston engine (US Patent No. 9,169,773). The air fuel ratio (AF) for a combustion process in internal combustion engines is generally expressed on a mass basis, defined as follows:

Where N is the number of moles and M is the molar mass. The molar mass of air is approximately 28.97 g/mol. The molar mass of methane is 16.04 g/mol. In complete combustion of a hydrocarbon fuel, all of the carbon in the fuel is converted to carbon dioxide and all the hydrogen forms water. When the minimum amount of air is used for complete combustion, the process is described as stoichiometric combustion. Dry air can be approximated as consisting of 21 % oxygen and 79% nitrogen, or in molar terms 3.76 moles of nitrogen per mole of oxygen. The balanced chemical reaction for stoichiometric combustion of methane in dry air is accordingly:

CH + 2(0 ₂ + 3.76N ₂ )→ C0 ₂ + 2H ₂ 0 + 7.52N ₂

[0006] The stoichiometric amount of combustion air is accordingly 2 moles of oxygen plus 2 x 3.76 moles of nitrogen, for a total of 9.52 moles of air per mole of methane, which is an air fuel ratio of 17.19:

AF _{stoichiometric} = (9.52 x 28.97)/(1 x 16.04) = 17.19

[0007] The actual amount of air used in a combustion processes may be expressed in terms of the air-fuel equivalence ratio (lambda): AF _actual / AF _{stoichiometric} . The air-fuel equivalence ratio for an excess of air (a lean mixture), will be greater than 1 . The air-fuel equivalence ratio for a lack of adequate air (a rich mixture), will be less than 1 . The fuel-air equivalence ratio (phi) is the reciprocal of the air-fuel equivalence ratio: [0008] Compared to complete combustion (Rxn 2), the partial oxidation of methane to produce carbon monoxide and hydrogen (Rxn 3) uses ¼ of the stoichiometric amount of oxygen. CH ₄ + 20 ₂ → C0 ₂ + 2H ₂ 0 ... (Rxn 2) CH ₄ + O.50 ₂ → CO + 2H ₂ ... (Rxn 3)

[0009] The idealized air-fuel equivalence ratio for partial oxidation is accordingly ¼, and the air fuel ratio for idealized partial oxidation of methane in air is 17.19/4 = 4.2975.

[0010] In an autothermal reforming process, rapid exothermic complete combustion reactions (Rxn 2) are understood to be followed by slower endothermic reforming reactions, such as steam methane reforming (Rxn 4) and dry methane reforming (Rxn 5), ultimately yielding a synthesis gas comprising carbon monoxide and hydrogen:

CH ₄ + H ₂ 0≠ CO + 3H ₂ ... (Rxn 4) CH ₄ + C0 ₂ ≠ 2CO + 2H ₂ ... (Rxn 5)

[0011 ] There are numerous processes which utilize synthesis gas as a feed material for forming high value products. Synthesis gas can for example be used for the synthesis of oxygenated compounds such methanol, ethanol, formaldehyde, acetic acid or methyl acetate. Synthesis gas can also be utilized to produce liquid fuels and petrochemicals via the Fischer - Tropsch synthesis process. Synthesis gas can also be used as a precursor for processes that generate a relatively pure hydrogen gas stream using a water gas shift reactor and a membrane based separation system.

SUMMARY

[0012] A rotary internal combustion methane reformer is provided, comprising a housing having an intake port and an exhaust port. The housing defines a confined two-lobed epitrochoid space accessed by the ports, within which a three-sided rotor rotates eccentrically on a stationary gear so as to turn an output shaft through approximately 1080 degrees of rotation for every 360 degree rotation of the rotor. The rotation of the rotor within the housing is driven by a four step Otto cycle methane oxidation process carried out in working chambers defined by the rotor and the housing, so that the working chambers successively expand and contract to effect intake, compression, combustion and exhaust phases of the cycle. The combustion phase of the cycle typically involves spark initiated auto-thermal reformation of methane introduced through the intake port. This combustion may for example take place during an extended period of rotor motion, for example over approximately at least 100, 105, 1 10, 1 15 or 120 degrees of rotor rotation.

Combustion thereby produces a synthesis gas comprising carbon monoxide and hydrogen that is exhausted through the exhaust port.

[0013] In select embodiments, the reformer may be adapted so that at least some minimum threshold value of methane entering the reformer at the intake port is converted to oxidation products in the synthesis gas that is exhausted through the exhaust port, such as 50, 55, 60, 65, 70, 75, 80, 85, 90 or 95%.

[0014] The reformer may be adapted so that the combustion phase of each cycle takes place during a defined, relatively prolonged, combustion time period, for example being at least 5, 6, 7, 8, 9 or 10 milliseconds.

[0015] The reformer may be adapted so that the combustion phase of each cycle takes place at a selected combustion temperature, for example of 850 to 1400°C. Similarly, the reformer may be adapted so that the combustion phase takes place at a selected combustion pressure, for example of from 20 to 40 bars.

[0016] In select embodiments, the reformer may be adapted so that the back pressure at the exhaust port is above a threshold value, for example being at least 0.1 , 0.5, 1 , 5, 10, 20 or 30 barg.

[0017] In select embodiments, the reformer may be adapted so that the fuel entering the intake port comprises air and methane. In such embodiments, the air- fuel ratio may for example be variable between selected values, for example of from 4.29 to 17.19.

[0018] In some embodiments, the spark initiated auto-thermal reformation may for example be initiated by at least 2 spaced apart spark sources, and the multiple spark sources may provide sparks at different times.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 schematically depicts the operation of the Wankel Rotary Engine.

[0020] Figure 2 is a schematic illustration of a process for producing liquid fuels as well as petrochemicals via Fischer - Tropsch synthesis using a rotary engine reformer. [0021 ] Figure 3 is a schematic illustration of a process a for producing methanol using a rotary engine reformer.

[0022] Figure 4 is a schematic illustration of a process for producing hydrogen gas using a rotary engine reformer.

DETAILED DESCRIPTION

[0023] The attributes of a Wankel rotary engine are surprisingly well suited to carrying out auto-reforming reactions. A reciprocating piston engine has 180 degrees of crankshaft rotation per stroke (or 4 x 180 = 720 degrees per

thermodynamic cycle) while a rotary engine nominally has 270 degrees of eccentric shaft rotation per equally segregated "stroke" (or 4 x 270 = 1080 degrees per thermodynamic cycle). In effect, for any given shaft rotation rate, the rotary engine nominally has 1 .5 times more time to accomplish each stroke (the output shaft spins three times as fast as the rotor). In practice, the Wankel compression and combustion strokes may be prolonged, by virtue of inlet and exhaust port geometry, and may for example occupy up to approximately 120 degrees of rotor (not shaft) rotation. Also, and there is less combustion chamber volume variation in the last phase of combustion/expansion, for example during up to approximately the last 30 degrees of the combustion phase (see Cheng-Hsiung Kuo, Huai-Lung Ma and Chien-Chang Chen, Journal of C.C.I .T., VOL.32, N0.1 , Nov., 2003, Chamber

Contour Design and Compression Flow Calculations of Rotary Engine; and, Baowei Fan, Jianfeng Pan, Wenming Yang, Hui An, Aikun Tang, Xia Shao & Hong Xue, "Effects of different parameters on the flow field of peripheral ported rotary engines, Engineering Applications of Computational Fluid Mechanics Vol. 9 , Iss. 1 , 2015). With prolonged compression and combustion phases, the exhaust and intake strokes may be shortened, for example approximately sharing the remaining 120 degrees of rotor rotation. In effect, the combustion phase may be adapted to last for up to approximately 1/3 of the rotor rotation, and the last phase of combustion takes place as a relatively isochoric process. The increased combustion cycle time, and the approximately isochoric combustion period, together afford an improved opportunity for partial oxidation reactions to come to an equilibrium, favoring the production of carbon monoxide and hydrogen, for example by steam methane reforming reactions (Rxn 4) and/or dry methane reforming reactions (Rxn 5), rather than exhausting hot unburnt fuel.

[0024] For example, in a Wankel engine at a shaft speed of 5000 rpm, the rotor speed will be approximately 1 ,666 rpm, or 27 rotations/second, taking 36 milliseconds/revolution, and affording 12 milliseconds for the combustion phase of each cycle including a relatively isochoric period of 3 milliseconds. In contrast, in a piston engine operating at 5000 rpm, the pistons move up and down once for every shaft rotation, and the duration of the combustion downstroke is accordingly only 6 milliseconds, with no significant isochoric period. At 8000 rpm, approaching typical maximums for production engines, a Wankel engine still affords 7.5 milliseconds for each combustion phase, which is 25% longer than in the piston engine operating at 5000 rpm.

[0025] Equilibrium reactions are also favored in a rotary engine by virtue of turbulence in the air-fuel mixture. The level of turbulence in a piston engine is necessarily limited, whereas the relatively high flow velocity of combustion gases in a rotary combustion chamber, in which the chamber moves at a substantial velocity relative to the combustion chamber boundaries, creates significant turbulence (see Fan, et al., 2015, op. tit).

[0026] Each face of the rotor is provided with a "rotor depression" which provides a path for the partially burned air-fuel mixture to navigate the otherwise narrow clearance between the rotor housing and rotor. Adjusting the shape of the rotor depression accordingly provides a means for confining the partial

oxidation/combustion chamber. The shape of this chamber can accordingly be tuned to optimize partial oxidation. The rotor depression also provides for a combustion chamber with a relatively high surface to volume ratio, increasing the effectiveness of any autothermal reforming catalyst deposited on the rotor depression.

[0027] In a Wankel rotary engine, the cycles of intake, compression and combustion take place in distinct regions of the two-lobed epitrochoid space, as the three-sided rotor rotates. This inherently reduces the risk of premature auto-ignition of the fuel-air mixture, which in a piston engine is subjected during compression to the residual heat present in the combustion chamber (compression and combustion taking place in the same cylindrical space). Also, the lower compression ratio of a typical Wankel engine results in a lower combustion temperature, and thereby provides a higher H ₂ /CO ratio.

[0028] In select embodiments, rotary reformers make use of the typical double consecutive spark ignition system of the Wankel, providing tow (or more) sparks in each combustion cycle. The timing and position of these sparks may accordingly be adapted to increases the methane conversion rate - for example compared to a typical piston engine.

[0029] Further, there is effectively no overlap between intake and exhaust ports in modern Wankel engines, a feature which in an operating rotary reformer results in nearly complete depletion of the syngas from the engine in the exhaust phase (or "stroke"). This is in contrast to the necessary presence of a dead volume on top of a reciprocating piston, which leaves burnt gases un-exhausted and carried over to the intake stroke.

[0030] In select embodiments, a rotary reformer may be operated with a relatively higher back pressure on the exhaust. Wankel engines are relatively insensitive to exhaust back pressure, a feature that is related to minimization of dead space and the relatively complete exhaust cycle of the Wankel. The relatively high pressure of the exhausted reformed gas may for example be used in downstream processes, in some cases obviating the need for a compressor. In contrast, the ability to apply backpressure in a piston engine is limited, in part because of problems that arise because of the sealing mechanism around valve seats.

[0031 ] The combustion chamber of a rotary engine has a higher surface area to chamber volume ratio than a reciprocating engine, and its shape results in a longer flame travel distance. In addition, the trailing section of the combustion chamber where final or secondary combustion occurs is a narrow, wedge-shaped section which has the capacity to quench combustion. The higher combustion chamber surface to volume ratio means that there is a greater, relatively cool, wall area which also has the capacity to quench combustion (reducing peak temperatures and pressures in the combustion chamber). This typically results in a high quenching effect at the trailing portion of the charge. During combustion, the charge is swept forward by the moving chamber at relatively high velocity, facilitating turbulent mixing of gases. In effect, This reduces the octane requirement of the engine. Accordingly, these characteristics dictate that a rotary engine will generally accommodate fuels having a modest octane number requirement, in comparison to the compression ratio, and a corresponding ability to burn a variety of fuel mixtures, such as fuels with lower calorific value, for example landfill gases.

[0032] An often reported disadvantage of Wankel engine is relatively high carbon monoxide emissions, which may for example necessitate catalytic treatment of the exhaust. This disadvantage becomes a benefit for reforming systems, in which the carbon monoxide is a desired product of the process

[0033] The operation of a typical Wankel Rotary engine utilizing gasoline or a gaseous fuels is for example described in US Patent Nos 4,926,816 and 5,392,740. In general terms, a Wankel Rotary engine (Figure 1 ) can consist of two or more separate housings, each containing a symmetric three faced rotor. The rotary motion of multiple rotors in the engine is offset and coupled through the eccentric shaft. An oxidant-fuel mixture is passed into the combustion chamber through a fuel mixer and trapped between one face of the rotor and the walls of the combustion chamber. The motion of the rotor in the combustion chamber compresses the gas mixture between the wall and the rotor face. One or, more typically two, spark plugs are located at the point of highest compression of the fuel air mixture, operating to ignite the mixture. The ignition of the oxidant-fuel mixture initiates the combustion or partial combustion reactions (Rxn 2 and 3 respectively) which being exothermic release large amounts of heat. The equilibrium of the reforming reactions (Rxn 4 and Rxn 5) influences the final distribution of the synthesis gas products. Driven by these reactions, the rotor moves forward generating mechanical power through the connected eccentric shaft arrangement, while simultaneously allowing the product gas mixture to expand and cool.

[0034] In Figure 1 , the phases of an Otto cycle in a rotary engine are illustrated. In Part 1 of Figure 1 , face C of the rotor is about to initiate the intake phase, while face A of the rotor has completed the intake phase and is about to initiate the compression phase. Face B of the rotor in Part 1 of Figure 1 has completed the post combustion expansion phase and is about to initiate the exhaust phase. In Part 2 of Figure 2, face C is in the middle of the intake phase, face A is in the middle of the compression phase, and face B has initiated the exhaust phase with the combusted gas exiting through the exhaust port. In Part 3 of the Figure, face A has completed the compression phase and the spark has ignited the fuel-oxidant mixture. Face C and B are in the middle of the intake and exhaust phases respectively. In Part 4 of the Figure, face A has completed the combustion phase and the expansion phase has been initiated.

[0035] In certain embodiments, one spark plug ignites the oxidant - fuel mixture in the combustion chamber prior to the gas mixture attaining maximum

compression. In such an embodiment, the partial oxidation or combustion reactions are active while compression is occurring. At or after the point of maximum compression, the second spark plug is activated, so as to facilitate completion of the combustion or partial oxidation reactions. The flame from the combustion provides a medium for the progression of secondary reactions in the system such as the steam methane reforming or dry methane reforming (Rxn 4 and 5 respectively).

[0036] In certain embodiments, the oxidant-fuel mixture is compressed to the maximum value, at which point the first spark plug is activated to ignite the oxidant- fuel mixture. The combustion and partial oxidation reactions occur while the rotor moves forward and releases the pressure on the gaseous system. The second spark plug is activated during the decompression process. This may be adapted to facilitate completion of the combustion or partial oxidation reactions. Alternatively, the spark may allow a medium for the progression of secondary reactions in the system such as the steam methane reforming or dry methane reforming (Rxn 4 and 5 respectively).

[0037] In certain embodiments, the oxidant-fuel mixture is compressed to the maximum value, at which point both the spark plugs are activated simultaneously to ignite the air-fuel mixture. Alternatively, both the spark plugs may be activated before or after this point simultaneously, to ignite the air-fuel mixture.

[0038] In some embodiments, the fuel - oxidant mixture is fed to the

combustion chamber at ambient conditions, for example at approximately 25 °C. Following the combustion or partial combustion reactions, the exhaust gas is decompressed and exits the combustion chamber at or above ambient pressure.

[0039] In some embodiments, the fuel-oxidant mixture is fed to the combustion chamber at pressures above ambient, for example at 0-3 barg and temperatures ranging from 0 °C to over 100°C. Following the combustion or partial combustion reactions, the exhaust gas is decompressed and exits the combustion chamber at or above ambient pressure. In select embodiments, the exhaust gas may be utilized to operate a turbocharger.

[0040] In some embodiments, following the combustion or partial oxidation reactions, the exhaust gas is decompressed to a pressure higher than inlet pressure. The products of the combustion exit the engine at elevated pressures, for example up to 30 barg. Expanding the products of combustion to pressures higher than the inlet pressure decreases the power produced by the engine and increases the temperature of the syngas.

[0041 ] In embodiments utilizing more than one rotor, one combustion chamber may operate under complete combustion conditions, for example using a variety of fuels, such as methane or gasoline, while the other combustion chamber operates in a partial oxidation mode. In some embodiments, the exhaust from the chamber operating under partial oxidation conditions can be regulated to provide an exhaust flow at relatively high outlet pressures.

[0042] In some embodiments, the thermal energy available in the exhausted syngas may be recovered, for example using Stirling engine or Organic Rankine Cycle and generate mechanical or electrical energy. Alternatively, the heat recovered from the syngas can be utilized for making steam or generating cooling load using absorption chillers.

[0043] In select embodiments, the fuel for the process can generally be any gas containing CH4 as a major constituent, for example natural gas, flare gas and biogas. The oxidant for the process can for example be air, or oxygen enriched air, or pure oxygen. Oxygen enriched air can for example contain a nitrogen to oxygen ratio ranging between 3.76 and 0. Mixtures of fuel to oxidant having CH :0 ₂ ratios ranging from 0.5 to 2 can for example be fed to the combustion chamber through the intake manifold of the engine. A diluent in the form of water, tail gas, nitrogen, argon, C02 or a combination of these gases can for example be added to the air- fuel mixture for the purpose of temperature control, and/or as well as reaction control. Similarly, water, tail gas or C02 may be used not be merely inert diluents, but as reactants themselves. In this context, tail gas may include the un- condensable component of the product mixture obtained from the Fischer-Tropsch synthesis reactor system downstream of the engine reformer. [0044] In certain embodiments, the oxidant-fuel mixture is premixed and sent into the combustion chamber through the intake manifold/port of the engine. The oxidant-fuel mixture may be optimized such that the system has sufficient oxygen to sustain the combustion flame for the entire mixture to undergo reaction, but at the same time, not enough to allow complete combustion of CH to form C0 ₂ and H ₂ 0. The exhaust gas will in general contain a mixture of CO, C0 ₂ , H ₂ and H ₂ 0, with small amounts of CH and other gaseous hydrocarbons.

[0045] Some embodiments may have a water gas shift reactor downstream of the exhaust gas stream to adjust the H ₂ :CO ratio in the exhaust gas from the system. In some embodiments, additional steam or water may for example be injected into the water gas shift reactor along with the exhaust gas from the reformer to obtain a synthesis gas product with H ₂ :CO ratio value between 2 and 2.1 in accordance with requirements of certain downstream processes, such as the Fischer-Tropsch synthesis process or a methanol synthesis process.

[0046] In some embodiments, the exhaust gas from the engine reformer may be cooled, pressurized and C0 ₂ /H ₂ S removed in accordance with requirements of certain downstream processes, such as the Fischer-Tropsch synthesis process or the methanol synthesis process.

[0047] In some embodiments, the fuel gas may for example be cleaned of H ₂ S and excess C0 ₂ using pressure swing adsorption, Selexol® or Rectisol® solvent base absorption or other technologies for acid gas removal. Alternatively, in some embodiments no gas cleanup system will be utilized either upstream or downstream of the engine reformer. In this case, the fuel gas may for example be mixed with an oxidant and fed to the engine reformer directly. The exhaust gas containing CO, C0 ₂ , N ₂ , H ₂ and H ₂ 0, with small amounts of CH and other gaseous hydrocarbons may be cooled to remove the H ₂ 0. In some embodiments, the tail gas of the downstream process may be mixed with the original feed fuel gas and recycled to the engine reformer. Similarly, in some embodiments, multiple engine reformers can be made to operate in parallel to process a larger quantity of fuel. MODEL DESCRIPTION

[0048] The model described as follows has been used to exemplify the operation of the rotary reformer. [0049] The notations for the model are as follows: engine volume capacity (Capacity _engine ); the engine speed in revolutions per minute (Speed _rpm ) and revolutions per second (Speed _rps ); the volumetric turnover (V _engine ); torque of engine (τ); power of engine (P _engine )] compression ratio of turbo (CR _Turb0 ); compression ratio of engine(CR _engine ); enthalpy of component i at temperature T and pressure P (Hi (T, P)); entropy of component i at temperature T and pressure P (S ₍ (r, P)); specific heat of component i at temperature T for constant pressure (C _P . (T)) and for constant volume(C _Vi (7)); specific ratio of gas mixture at stage at constant pressure (C _Pmix,j ) and at constant volume (C _Vmix] ); total energy of gas mixture flowing per second at the start of stage j of engine rotor cycle (Energy _j,in ) and at the end of the same stage (Energy j _01it ); heat capacity ratio at stage j (^); power of the turbocharger (Power _Turbocharger ); equilibrium constants for reaction r expressed in terms of fugacity(K _{R r} )and in terms of partial pressure partial pressure and mole

fraction of component i (p _t ) and (X _t ) respectively; molar flow rate of component i (F _t ) ; Enthalpy, Entropy and Gibb's Energy change of reaction r (AH _Rr ), ( AS _Rr ), (AG _Rr ) respectively;

Stage 1 - Turbo Charger unit: Gaseous fuel and air mixture entering the turbo charger unit at temperature and pressure respectively, and exiting the turbo charger unit at temperature and pressure respectively

Stage 2 - Compression stage of rotary engine: Gas mixture entering the rotary engine at temperature and pressure respectively and undergoing adiabatic

compression at the compression stage. The temperature and pressure of the gas mixture at the end of this stage is respectively.

Stage 3 - Combustion stage of rotary engine: The gas mixture entering at temperature and pressure respectively, is ignited by means of a spark

to undergo the combustion reaction (Rxn 2) and partial oxidation reaction (Rxn 3), which would in turn provide energy for the steam methane reforming and dry methane reforming reactions (Rxn 4 and 5 respectively). The combustion is isochoric. It is assumed the oxygen is consumed to completion in the first two reactions. The water gas shift reaction also takes place in the forward or reverse direction depending on the temperature of the gas mixture as well as the partial pressures of the components. The CO, C0 ₂ , H ₂ , H ₂ 0 and CH are then balanced by considering the equilibrium constants of Rxns 1 , 4 and 5. The temperature and pressure of the gas mixture at the end of this stage is respectively.

The temperature is determined by considering an energy loss factor

Stage 4 - Decompression Stage: The combustion gas mixture beginning this stage at temperature and pressure respectively, is decompressed and

allowed to exit the engine through the exhaust port at temperature and pressure respectively.

The efficiency of decompression or mechanical efficiency can be represented as

Where, s the ideal energy flow for 100 % efficiency

The power released during decompression is

The power consumed during the functioning of the rotary engine

is

The net power outpu from the operation of the engine is

EXAMPLES EXAMPLE 1 : Rotary Reformer and Fischer-Tropsh Reactor

[0050] This example illustrates a modeled process, implemented as set out above, that involves integrating a 1 .3 L Wankel rotary engine reformer with a Fischer - Tropsch synthesis reactor, using 100 % CH as reforming feed at atmospheric pressure and 25°C as the inlet conditions to the reformer. Air is used as the oxidant. Both combustion chambers of the rotary engine reformer are operating under partial oxidation condition. No gas cleanup system is applied. The mechanical efficiency of the engine is modeled to be 85%. The engine is modeled operating at 5000 rpm with a compression ratio of 7.65: 1 .

[0051 ] A schematic diagram for such a process is presented in Figure 2. As modeled, a mixture of 1 .07 mol/s of CH and 3.3 mol/s of air (Stream 101 ) is fed to the rotary engine reformer to generate a synthesis gas mixture (Stream 102) containing CH , C0 ₂ , CO, H ₂ , H ₂ 0 and N ₂ flowing at 4.37 mol/s at a temperature 836 °C and a pressure of 4.7 barg. This represents an air fuel ratio of 5.57, approaching the idealized AF = 4.29 for partial oxidation:

AF = (3.3 x 28.97)/(1 .07 x 16.04) = 5.6

The corresponding air-fuel equivalence ratio (λ) is 5.58/17.19 = 0.324, representing an exceptionally rich mixture (φ = 3.076). In select embodiments, the AF can for example be varied between 4.29 to 17.19.

[0052] The mechanical motion of the rotor is coupled with a power generator to offset the energy requirement in the overall process loop. The mechanical power generated by the engine is 15.22 kW. The synthesis gas mixture is allowed to cool to 350 °C in a heat exchanger and the cooled synthesis gas (Stream 103) passes through a water gas shift reactor. The water gas shift reactor increases the H ₂ :CO ratio of the synthesis gas to 2.1 and the gas (Stream 104) is then sent to a chiller to cool to 25°C. The compositions of the gas streams 101 , 102 and 104 are presented in Table 1 . Table 1 . Composition of fluid streams in process illustrated in Figure 2.

[0053] As modeled, the cooled synthesis gas (Stream 105) is pressurized to 30 bars in a compressor. A compressor operating at 100 % efficiency would require 34.62 kW for this compression. The compressed synthesis gas (Stream 106) is passed through a heat exchanger (HX1 ) to reach a temperature of 200 °C. The preheated synthesis gas (Stream 107) is fed to the Fischer - Tropsch Synthesis reactor to form a product stream (Stream 108) comprising of hydrocarbons, oxygenates and water. A wax stream (Stream 109) is separated from the product mixture in a separator maintained at 200 °C. The remaining product stream

(Stream 1 10) is passed through HX1 and then a chiller to cool the product to 25 °C. The cooled product stream (Stream 1 12) contains a mixture of gas and liquid phases, and is sent to a separator to split the stream into three parts - an aqueous phase containing oxygenates and water (Stream 1 13), a hydrocarbon rich liquid phase (Stream 1 14) and tail gas containing unreacted synthesis gas and short chain hydrocarbons (Stream 1 15).

[0054] The mechanical power generated by the engine reformer is 15.22 kW, while the power required for the compression of Stream 105 to 106 is 34.62 kW. The compression can be split into 2 stages with a cooling stage in the middle. The first compressor would increase the pressure of the stream by 5.5 bar, while the second stage compressing the gas to 30 barg. Assuming 80 % efficiency of operation of the compressors, the power required for Stage 1 and 2 compressors would be 15.14 kW and 21 .94 kW respectively. The engine reformer could be coupled with the Stage 1 compressor to offset the power requirement of the gas loop.

[0055] The product out of the Fischer - Tropsch reactor (Stream 108) is presented in Table 2.

Table 2. Properties of Fischer - Tropsch Synthesis reactor product

EXAMPLE 2: Rotary Reformer and Methanol Synthesis Reactor

[0056] This example illustrates a modeled process involving a 1 .3L rotary engine with one combustion chamber operating under complete combustion conditions and the second chamber operating under partial oxidation conditions, with both chambers using natural gas with 98% CH and 2% C0 ₂ as a fuel. The engine operates with a coupled turbocharger compressing the gas by a factor of 2. The exhaust from the chamber running partial oxidation is utilized downstream for methanol synthesis reaction. The exit pressure of the exhaust gas from the partial oxidation chamber of the reformer engine is set at a pressure of 30 barg. Air is used as the oxidant. A Selexol® solvent based gas cleanup system is applied

downstream of the engine reformer. The mechanical efficiency of the engine is considered to be 85%. The engine is operating at 7500 rpm and has a compression ratio of 7.65.

[0057] A schematic diagram for such a process is provided in Figure 3. A mixture of 36.42 sLps (standard litres per second) of natural gas and 1 10.43 sLps of oxidant (Stream 101 ) is fed to one chamber of the rotary engine reformer to generate a synthesis gas mixture (Stream 103) containing CH , C0 ₂ , CO, H ₂ , H ₂ 0 and N ₂ flowing at 189.95 sLps at an exit pressure of 30 bar. The air fuel ratio is accordingly: AF = (1 10.43 x 28.97)/(36.42 x 16.04) = 5.5.

[0058] Concurrently, a mixture of Natural gas and air (Stream 102) is passed through the second chamber of the engine reformer to undergo complete combustion. The combustion reaction in this chamber powers the rotation of the rotor in the partial oxidation chamber. Stream 104 is the exhaust gas from the combustion chamber and contains C0 ₂ , N ₂ , H ₂ 0 and unreacted 0 ₂ . The synthesis gas mixture from the partial oxidation chamber (Stream 103) is exhausted at 30 barg and allowed to cool to 350°C in a chiller and the cooled synthesis gas (Stream 105) pass through a water gas shift reactor. The water gas shift reactor increases the H ₂ :CO ratio of the synthesis gas to 2.1 and the gas (Stream 106) is then sent to a chiller to cool to 25°C. The compositions of the gas streams 101 , 103 and 106 are presented in Table 3.

Table 3. Composition of streams 101 , 103 and 106 in Example 2.

[0059] The cooled and compressed gas (Stream 107) is sent to a gas - liquid separator to remove the condensed water (109). The dehydrated synthesis gas stream (Stream 108) undergoes sulfur removal using a Selexol® based absorption bed system. The clean gas (Stream 1 10) is preheated to 180°C (Stream 1 1 1 ) and fed to the Methanol Synthesis reactor. The product coming out of the reactor (Stream 1 12) is a mixture of unreacted synthesis gas and methanol product.

Stream 1 12 is cooled in the heat exchanger (Stream 1 13) and a chiller in sequence to cool the product to 25°C (Stream 1 14). Stream 1 14 is passed through a Gas - Liquid Separator to separate the methanol as a liquid product (1 15) from the unreacted synthesis gas product (Stream 1 16).

Table 4. Composition of Stream 1 12 in Example 2

EXAMPLE 3: Rotary Reforming of Landfill Gas

[0060] This example illustrates a modeled process involving A 1 .3L rotary engine with one combustion chamber operating under complete combustion condition and the second chamber operating in partial oxidation condition. Gasoline is utilized as a fuel for the chamber having complete combustion, while landfill gas is utilized as the fuel for the chamber having partial oxidation condition. The composition of the landfill gas is CH : C0 ₂ : N ₂ 53:35: 12, along with sulfur based impurities. The engine operates with a coupled turbocharger compressing the gas by a factor of 2. The exit pressure of the exhaust gas from the partial oxidation chamber of the reformer engine is set at a pressure of 30 bar. Oxygen enriched air is used as the oxidant. A dual stage gas cleanup system based on Selexol® solvent is applied downstream of the engine reformer to remove C0 ₂ in one stage and sulfur compounds in the other. The remaining gas is passed through a membrane based separation system to obtain a clean H ₂ stream. The engine is operating at 7500 rpm and has a compression ratio of 7.65.

[0061 ] A schematic diagram for such a case has been presented in Figure 3. As illustrated, 148.64 sLps of air (Stream 101 ) is compressed to 30 barg (Stream 102) and passed through an oxygen selective membrane. The retentate (Stream 103) is 80.69 sLps of 95 % N ₂ and the permeate (Stream 104) contains 40% 0 ₂ and 60% N ₂ . The oxygen enriched air stream is mixed with 78.89 sLps of landfill gas along with some amount of moisture (Stream 105). The mixture of landfill gas and oxidant (Stream 106) is fed to one chamber of the rotary engine reformer to generate a synthesis gas mixture (Stream 108) containing CH , C0 ₂ , CO, H ₂ , H ₂ 0 and N ₂ flowing at 169.07 sLps at an exit pressure of 30 bar. Concurrently, gasoline (Stream 107) is passed into the second chamber of the engine reformer through the fuel mixer along with air to undergo complete combustion. The combustion reaction in this chamber powers the rotation of the rotor in the partial oxidation chamber. Stream 109 is the exhaust gas from the combustion chamber and contains C0 ₂ , N ₂ , H ₂ 0 and unreacted 0 ₂ . The synthesis gas mixture (Stream 108) is cooled by quenching with water (Stream 1 10) and the mixture (Stream 1 1 1 ) is sent to a water gas shift reactor to obtain an H ₂ :CO ratio of 10 (Stream 1 12). The composition of Stream 106, 108 and 1 12 is provided in Table 5. Stream 1 12, is cooled in a chiller to 25°C (Stream 1 13) and passed through a vapor liquid separator to remove the moisture (Stream 1 14). The remaining gas (Stream 1 13) is compressed to 30 barg and made to undergo a dual stage Selexol® based separation system to remove 23.90 sLps of C0 ₂ (Stream 1 15) and H _s S impurities (Stream 1 16). The remaining synthesis gas mixture (Stream 1 17) is made to pass through a H ₂ selective membrane to obtain 62.26 sLps of pure H ₂ (Stream 1 18) along with the retentate stream (Stream 1 19).

Table 5. Composition of streams 106, 108 and 1 1 1 in Example 3.

CONCLUSION

[0062] Although various embodiments of the invention are disclosed herein, many adaptations and modifications may be made within the scope of the invention in accordance with the common general knowledge of those skilled in this art. Such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way.

Numeric ranges are inclusive of the numbers defining the range. The word

"comprising" is used herein as an open-ended term, substantially equivalent to the phrase "including, but not limited to", and the word "comprises" has a

corresponding meaning. As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a thing" includes more than one such thing. Citation of references herein is not an admission that such references are prior art to the present invention. Any priority document(s) and all publications, including but not limited to patents and patent applications, cited in this specification are

incorporated herein by reference as if each individual publication were specifically and individually indicated to be incorporated by reference herein and as though fully set forth herein. The invention includes all embodiments and variations substantially as hereinbefore described and with reference to the examples and drawings.