Patent Application
20250129304
Biomass gasification is a process that converts an organic carbonaceous matter like woody biomass, agricultural residues, and municipal solid waste into combustible gaseous mixture containing Hydrogen, Carbon Monoxide, Methane, Carbon Dioxide and Nitrogen, by reacting the biomass feedstock with controlled amount of oxygen and steam in various proportions and over a range of temperatures. Hydrogen rich syngas is the key product of such a gasification process that may be further processed to generate pure Hydrogen of desired quality and gaseous mixture of desired composition for subsequent downstream use. The Hydrogen so generated may be used in a variety of applications like Fuel Cells (both PEM and SOFC), Internal Combustion Engines, Gas Turbines etc. At the same time, the desired composition-syngas mixture may be used for downstream chemical synthesis through catalytic reforming and use in energy conversion devices like Fuel Cells (SOFC), Internal Combustion Engines, Gas Turbines etc. With Hydrogen being the key compound in the downstream gas, configuration and operational efforts aim to enhance the throughput gas Hydrogen content. The essential design and operational controls are to maximize the generation rate of Char in the reactor and then enhance utilization of Char generated in the gasifier to mitigate the “Carbon Boundary”. Beyond the carbon boundary, the system operation ceases in time.
The detailed description is presented with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.
In recent years, rapid technological advancements have led to an unprecedented increase in energy requirement, as a result of which more and more energy sources are being developed or researched to fulfil the requirement. Further, emission of CO2 has induced climate change affecting every aspect of life on an unprecedented scale which raises a need to emphasis on “green” energy resources. One of such green energy source is combustible gaseous products produced by gasification of carbonaceous matter like woody biomass, agro-residue and municipal solid waste.
As would be generally understood, gasification is a process by which either a solid or liquid carbonaceous material, containing chemically bound carbon, hydrogen, oxygen, and a variety of inorganic and organic constituents, is reacted with either air or mixture of oxygen and steam to provide sufficient exothermic energy to produce a primary gaseous product containing mostly H2, CO, CH4, CO2, N2, H2O(g) and volatile and condensable organic and inorganic compounds. In one example, the material used during gasification may be a biomass substance, which in most of the cases like agro residue, packing wood waste, saw dust etc considered as waste, containing 5-30% moisture. Examples of biomass substance include, but may not be limited to, forest slash, urban wood waste, lumber waste, wood chips, sawdust, straw, firewood, agricultural residue, and the like. Specifically, in biomass gasification, biomass is gasified in presence of steam and/or oxygen to produce “synthesis gas”, rich in CO and H2, which in turn may be, by appropriate separation process and subsequent catalytic process, converted to high-value fuels and chemicals.
As may be understood, the system converting carbonaceous matter into combustible gas is known as a gasifier or a gasification system, such as an open top downdraft gasifier system with air as gasifying media, a reburn gasifier system with multiple reactant entry points, etc. For brevity, we here only discuss characteristics of the reburn gasifier system with multiple reactant entry points operated in either open top or closed top, as the case may be, which includes a cylindrical reactor receiving biomass form the top and discharging gas from the base and also include multiple nozzles along the length of the reactor for introducing different reactant mixtures, which acts as the gasification media. In an example, the cylindrical reactor may be virtually divided in several zones based on the reactions taking place in that zone such as a drying zone, a pyrolysis zone, a combustion zone and a reduction zone. During gasification, the reactor is initially loaded with charcoal from the bottom up to the level above the combustion zone and topped up with biomass feedstock.
Thereafter, the char bed in the vicinity of side nozzles is ignited through external source, which subsequently starts thermochemical reactions inside the reactor leading to self-sustaining operation as auto thermal mode of operation. Once the char bed is ignited, initially, the fresh biomass at the top is dried up due to the heat generated and the heat transfer through radiation and convection from the hot char bed resulted in formation of the drying zone. Then, the dried biomass is subjected to high-temperature condition which results in pyrolysis of biomass feedstock to convert biomass in gaseous products comprising of CHO complex and carbon as char. Based on the oxidizer/reactants availability inside the reactor, the gaseous products also undergo combustion resulting in heat release rendering the system auto thermal.
Thereafter, the products of pyrolysis, i.e., higher hydrocarbons, gaseous mixture and char, pass through the a zone where volatile react with the oxidiser identified as combustion zone where combustion of a portion of the hydrocarbons/gases/char takes place resulting in high temperature, around 1200° C. in the reactor. Under the conditions of such high temperature, the higher hydrocarbons have a tendency to breakdown to low molecular weight hydrocarbons resulting in relatively clean gas being generated. Thereafter, the gases and solid char move downwards where reaction of char with H2O and CO2 indentified as reduction zone, takes place. Finally, the products of gasification exit from the base and a known quantify of char is positively extracted through an appropriate mechanism.
The typical thermochemical reactions taking place along the length of the reactor of the gasification system are presented in below Table 1. It may be noted from below table that, the carbon reaction with steam (R2) and Carbon Monoxide reaction with Steam (R9) are the principal hydrogen generating reactions.
It is important to note that, the gasification system is operated over a range of operating condition, in which the variations primarily being with steam to biomass ratio (SBR). Other parameters include the equivalence ratio (fuel/oxidiser to stochiometric) and the Oxygen-steam mixture injection temperature. As may be understood from hydrogen generation reaction, i.e., R2 and R9 that, the main element required in an adequate amount for higher hydrogen yield is steam concentration (i.e. H2O concentration) and the char (i.e. Carbon concentration) generated due to pyrolysis and combustion. In an example, with higher steam concentration, one mole extra hydrogen is generated from steam itself which further leads to reducing consumption of biomass as well. So, for increasing the hydrogen generation capacity of the gasification system, SBR needs to be high.
However, as the SBR increases, the char consumption increases, i.e., generated char is consumed at a higher rate, due to which the sustained operation of the gasification system is sacrificed. It may be noted that for sustained operation a of gasification system to produce hydrogen-rich syngas, the gasification system needs to be operated inside an important parameter called—a Carbon Boundary Limit (CBL). The CBL represents the point at which the rate of char generation is equal to the rate of char consumption. The CBL is a strong function of Steam to Biomass (typically on mole ratio basis) for a given equivalance ratio of oxidiser concentration. As the CBL increases, the Char consumption rate due to Char-Steam reaction increases and if the Char consumption rate increases beyond the generation rate, over time the char produced gets consumed resulting in a ceasing of the gasifier operation to produce combustible gases.
So, for extending CBL beyond its conventional limit, the char generation rate needs to be higher. As may be understood, the char generation solely depends on the rate of pyrolysis which in turn further depends on the temperature profile inside the reactor. Higher the temperature, faster will be the pyrolysis and hence the higher the char generation rate. Such required heat is provided by the energy released by the combustion of volatile species/gases and carbon/char inside the reactor. The temperature of Oxygen-Steam mixture also play a critical role in establishing the temperature profile inside. The higher the mixture temperature, better will be pyrolysis and hence lower will be the endothermicity (heat requirement) for pyrolysis and related reactions to occur inside the reactor, thus improved the temperature profile. Thus supplying the Oxygen-Steam mixture at a higher temperature aids in the pyrolytic process.
Further, the injected oxy-steam mixture needs to be staged and distributed across the reactor and along the length of the reactor, with controlled temperature and equivalence ratio to increase the rate of combustion and hence heat release which in turn increases the temperature inside the reactor and as a commensurate effect the rate of char generation. The oxy-steam gasification key operating conditions of the conventional systems are presented in below Table 2.
However, the conventional methodologies, for example conventional system as described in Indian Patent Application 6783/CHE/2015 (or Indian Patent No. 390746) and techniques designed for gasification include injection points of steam/oxygen/mixture along the length of the reactor in a particular line, with the injection being flush with the reactor (closer to the wall inside the reactor). Due to this configuration, the oxy-steam mixture may not penetrate inside the reactor up to its axial axis and remains restricted to one particular zone along the length of the reactor. While the configuration may suffice for small diameter reactors (with inside diameter less than 100 mm), as the diameter increases (as in case of practical reactors ranging from few kWe level and higher), only a small sector along the length of the reactor receives the reactant mixture. This basically results in incomplete reaction of Char with the section diametrically opposite to the injection points having extremely limited accessibility to the reactants (Oxygen-steam mixture). As such even when steam in excess of CB limit is sent, complete Carbon conversion will not take place and the hot gas exiting the reactor will have substantially high moisture content. Basically the Hydrogen yield and system efficiency suffers. Further, there is no disclosure present in conventional gasification system, to appropriately managing the temperature and ratio of the oxy-steam mixture to increase the char generation rate inside the reactor. In the conventional system, the same quality mixture (in terms of temperature and Steam-Oxygen ratio) is injected into the reactor through all the ports. This restricts the ability to control the Char generation rate, especially when the biomass quality and type changes.
Examples of a biomass gasification system and method for producing hydrogen rich syngas from biomass, are described. The proposed biomass gasification system provides higher hydrogen yield for variety of biomasses by controlling and modifying the conventional ways of injection of oxy-steam mixture inside the gasification system. The biomass gasification system comprised of a gasification reactor. The gasification reactor further comprises an inlet, an outlet, and side walls disposed between the inlet and the outlet. In an example, the inlet is a lock-hopper based inlet positioned at the top of the gasification reactor isolating the gasification reactor from ambient air surrounding while charging gasification reactor. The outlet is positioned at the bottom end of the reactor for discharging products of gasification. In an example, the outlet is connected with a purification and analyzing system for purifying and analysing characteristics of the products of gasification.
The biomass gasification system further comprises a plurality of injectors positioned along the length of the gasification reactor for injecting oxy-steam gasifying media inside the reactor. In one example, the plurality of injectors are radially protruded inside the reactor up to a certain depth for appropriately providing the flow distribution of oxy-steam mixture across the gasification reactor for improving the pyrolysis zone height and rate. In another possible implementation, the plurality of injectors protruded inside the reactor may bend downward towards the side walls of the reactor by an angle to efficiently provide the oxy-steam mixture across most difficult locations of the gasification reactor to reach for. In one example, the gasification reactor is divided in multiple circumferential layers each having plurality of injectors positioned azimuthally separated by different arc lengths/angles subtending at the centre. In an example, the number of injectors, concentration of oxy-steam mixture, and quantity of mixture transferrable from injectors in each circumferential layer may vary based on the position of the circumferential layer along the lengthwise extension of the gasification reactor.
The biomass gasification system may further includes a plurality of thermocouples coupled to the gasification reactor along the length of the gasification reactor. The gasification system may also contain plurality of thermo-couples distributed azimuthally and protruding to different depths of the reactor. The plurality of thermocouples are used to monitor the temperature profile inside the reactor for providing appropriate temperature reading during the operation of the gasification system to efficiently determine the requirement of the reactor. Based on the determined temperature profile, the temperature of the oxy-steam mixture and the ratio of oxygen to steam is adjusted to provide adequate amount of reactant and hence energy or heat for increasing the rate of pyrolysis. Further, the biomass gasification system includes an ignition nozzle close to the bottom end of the gasification reactor for igniting the char bed inside the reactor for initiating the gasification process.
The above aspects, and advantages of the subject matter will be better explained with regard to the following description, appended claims, and accompanying figures. It should be noted that the description and figures merely illustrate the principles of the present subject matter along with examples described herein and, should not be construed as a limitation to the present subject matter. It is thus understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and examples thereof, are intended to encompass equivalents thereof. Further, for the sake of simplicity, and without limitation, the same numerals are used throughout the drawings to reference like features and components.
In an example, the purpose of the inlet 104 of the gasification reactor 102 is to allow loading of the biomass feedstock inside the gasification reactor 102 and is provided with a lock hopper. The lock hopper, as may be understood, provides a means for continuously feeding the gasification reactor 102 to ensure a leakproof charging of biomass feedstock into the gasification reactor 102 by isolating it from ambient air surrounding. On the other hand, the outlet 106 of the gasification reactor 102 is for discharging a produced mixture of gases and is coupled with a purification and analysing system for purifying the mixture of gases to retrieve a required gas from the mixture of gases.
The system 100 further includes a plurality of injectors 110-1, 2, 3, . . . , N (referred to as injectors 110) positioned along the length of the gasification reactor 102. The injectors 110 are meant for injecting gasification agents, such as oxygen, steam, or oxy-steam mixture, inside the reactor for enabling combustion of gases and char (charcoal). In an example, as shown in the expanded top view of the gasification reactor 102 in
In an example, the injectors 110 along the length of gasification reactor 102 are arranged in such a manner that the gasification reactor 102 is divided in multiple circumferential layers having certain width and each layer having certain number of injectors displaced and staggered circumferentially and azimuthally by an angle of deplacement from each other. For example, assuming the gasification reactor 102 to be divided into 3 layers from top end to the bottom end, 1st circumferential layer may include 3 injectors with 120° separation from each other, 2nd circumferential layer have same 120° separation between 3 of the injectors but these are displaced by an angle of 60° with respect to the injectors of the 1st circumferential portion, and the 3rd circumferential layer has 6 injectors having 60° separation each with certain displacement w.r.t to injectors of other layers. It may be noted that, the number of circumferential layer, number of injectors on each layer, and angle of separation between injectors of similar layer and other layers is exemplary and any other combination of these parameters may be used to get improved results without deviating from the scope of the present subject matter.
Further, the depth of insertion of the injectors 110 inside the gasification reactor 102 may vary with the maximum depth being the center of the gasification reactor 102 and minimum being the side walls 108. It may be noted that, the number of injectors 110, angle of separation between the injectors 110 and depth of injectors 110 inside the gasification reactor 102 in each circumferential layer may vary based on the position of the circumferential layer along the lengthwise extension of the gasification reactor 102. In another example, other features such as temperature profile and quantity of biomass inside the gasification reactor 102 may also effect the above disclosed features of injectors 110 in each circumferential layer without limiting the scope of the present subject matter. In another example, the diameter of opening of injectors 110 may vary to control the velocity of flow of gasification agent inside the gasification reactor 102.
The system 100 may further includes a plurality of thermocouples 112 coupled along the length of the gasification reactor 102. The plurality of thermocouples 112 are meant for measuring the temperature inside the reactor for determining a temperature profile of the reactor. As may be understood, that the temperature is the sole deciding factor for finding the amount of biomass disintegrates into char and gases because as high as the temperature inside the reactor reaches, more the biomass starts breaking into char and gases. So, for monitoring and for having a good look at the temperature variation, these plurality of thermocouples 112 help in analysing the temperature profile inside the reactor (the same will be discussed in upcoming figures). Further, the temperature readings of the plurality of thermocouples 112 may also be used for setting the temperature of injecting oxy-steam mixture to provide appropriate heat inside the reactor. The temperature readings may also be used to set the Oxygen-Steam ratio at particular injectors.
The system 100 may further include an ignition nozzle 114 located at the bottom of the gasification reactor 102 for igniting the biomass. In an example, the ignition nozzle 114 is located near to a char bed for igniting the bed for initiating the gasification process.
In an example, in operation, initially the charcoal is charged inside the gasification reactor 102 up to a combustion zone and the biomass feedstock is topped over that via inlet 104 up to a drying zone, and thereafter, the gasification reactor 102 is set into suction mode/negative pressure through the operation of the suction blower aided by the scrubbing nozzles (not shown in
In an example, the injectors 110 are further coupled to an oxy-steam supply 116. Instead of oxy-steam supply 116, the injectors 110 may also be coupled to multiple sources supplying oxygen and steam separately without deviating from the scope of the invention. In an example implementation, the injectors 110 while coupling with the oxy-steam supply 116 may mid-way coupled with a plurality of junction elements 118. In an example, the junction elements 118 enables controlling concentration of gasification agent flowing inside the gasification reactor 102. Further, these junctions 118 may enable mixing of oxygen and steam, when coming from different supply sources. The opening and closing of the junction elements 118 may be controller by valves based on the requirement of oxygen and steam inside the reactor, wherein the same may be controller automatically or manually based on the temperature profile. Therefore, the steam concentration in the oxy-steam mixture is varied to control the SBR of the gasification reactor 102 somewhere between 2.0 to 3.5. For example, initially the oxy-steam mixture contains higher concentration of oxygen and once char (i.e. Carbon (C)) starts forming inside the gasification reactor 102, the oxy-steam mixture with higher steam concentration is being injected to increase rate of water gas reaction.
Thereafter, based on the available oxy-steam mixture, the pyrolyzed char and gases further combust to generate heat which in turn accelerates the pyrolysis as it is dependent on the temperature inside the gasification reactor 102. It may be noted, with higher steam concentration, the Steam to Biomass Ratio (SBR) starts increasing which results in higher char consumption because now steam started reacting with both char and CO to generate hydrogen. So, it may be noted that at higher SBR, the hydrogen yield is increased unprecedently and char consumption increases as well. To maintain a balance inside the gasification reactor 102 it is required to increase char generation as well. The same is accomplished by injecting oxy-steam mixture up to a certain depth as well as height inside the gasification reactor 102 at certain injecting temperature and higher Oxygen to Steam ratio with the help of injectors 110 for increasing the rate of combustion which eventually increases the rate of pyrolysis. In this way, the CBL of the system 100 is extended beyond the conventional limit by increasing char generation. The complete spectrum of results corresponding to the oxy-steam injection using the system 100 is presented in Table 3. It may be noted that, with an increase in the SBR, the hydrogen yield per kilogram of biomass increases and the same is monotonous with SBR. Further, with increasing SBR, the fraction of Hydrogen contributed from steam increases.
While pyrolysis is going on, the output hydrogen rich syngas is being collected from the outlet 106. In an example, the outlet 106 is connected to a purification and analysing system (not shown in
In an example, as shown in the expanded top view of the gasification reactor 102 in
The system 200 may further include other components like thermocouples 112, ignition nozzle 114, oxy-steam supply 116, junctions 118, a scrubber, a gas analyser, a flow measuring device, and a burner similar to that of system 100.
The order in which the process 300 is described is not intended to be construed as a limitation, and any number of the described process blocks may combine in any order to implement the process 300, or an alternative process. It may be understood that the blocks of the process 300 may be implemented on any one of the systems 100, 200.
At block 302, a charcoal bed formed by loading charcoal is ignited through an ignition nozzle 114. For example, the ignition nozzle 114 present at a bottom end of the systems 100, 200 is used for igniting charcoal bed to provide initial startup to the gasification process. In an example, the ignition is performed using an external source of energy. In an example, initially, charcoal and a biomass feedstock are loaded inside the systems 100, 200. The charcoal is loaded up to a level of combustion zone to form the charcoal bed and the biomass feedstock is topped or loaded above the charcoal bed up to a drying zone. For example, the inlet 104 of the gasification reactor 102 is used to charge the gasification reactor 102. Examples of biomass feedstock include, but may not be limited to, forest slash, urban wood waste, lumber waste, wood chips, sawdust, straw, firewood, agricultural residue, and the like.
Once the char bed is ignited, it starts generating heat which in turn dries the up stocked biomass feedstock. Thereafter, the biomass feedstock undergoes pyrolysis and disintegrates into char and mixture of gases.
At block 304, a gasification agent is injected inside the gasification reactor through the plurality of injectors disposed circumferentially around the gasification reactor and along the lengthwise extension of the side walls of the gasification reactor and inserted at a certain depth inside the gasification reactor. For example, in case of system 100, the gasification agent is injected through the injectors 110 which are protruding radially inside the gasification reactor 102 for appropriately introducing the oxy-steam mixture over the char bed to increase the char generation and char consumption at the same time. While the gasification agent may also be injected inside the reactor through injectors 202 of the system 200 which are inclined at a certain angle with the side walls 108 of the gasification reactor 102.
In an example, the temperature, concentration ratio, and quantity of the gasification agent is varied based on the temperature readings of the thermocouples 112 or based on the requirement of hydrogen. For example, as the temperature inside the reactor increases, more biomass starts breaking which results in increase in the rate of generation of char, resulting in extended CBR. Now, the generated char may react with oxy-steam mixture according to reaction R2 and R9 to form hydrogen. In this way, CBR of the reactor is extended and the steam to biomass ratio is extended beyond its limit to increase the yield of the hydrogen. Further, it may be noted that, higher the SBR, more concentration of H2O is present and may react with CO to generate higher yield of H2. Hereinafter, all the thermochemical reaction may take place automatically inside the gasification reactor 102 to make it self sustaining over a period of time.
At block 306, a hydrogen-rich syngas is collected from the outlet 106 of the gasification reactor 102. For example, outlet 106 of the gasification reactor 102 is used to retrieve the generated hydrogen-rich syngas. In an example, the outlet 106 of the gasification reactor 102 is coupled with purification and analyzing system (not shown in
The following section is directed to provide various exemplary experimental results from
The above explained fact may be more clearly and explicitly established by comparing the magnitudes of contribution of respective reaction in generation of hydrogen.
From above discussion, it is observed that, the system operating at a higher steam fraction provides a distinct advantage in terms of the char bed promoting the water gas shift reaction and also acting as a reducing agent of H2O considering the same is performed at a temperature over 700° C. In order to determine if the current SBR concentration and injection temperature are enough to sustain the gasification process inside the gasification reactor 102, the temperature in the vicinity of the char zone is monitored carefully to determine a perfect combination between the injection temperature and SBR concentration which is explained in detail in conjunction with
Now, the mixture injection temperature is further increased to 727° C. while reducing the SBR from 3.4 to 2.9 which is presented in
Based on the graph depicted in
On analyzing performance parameters represented in table 5, it may be observed that the highest hydrogen yield per kilogram of biomass reported at the carbon boundary of SBR 1.5 with yield being 73 g/Kg at energy efficiency of 73.5% is increased to 110 g/Kg of biomass at SBR 3 and SBR energy efficiency of 62.5%. Further, in H2 yield, the contribution of steam has increased from 28% to 45%. Overall, by controlling mixture injection temperature, a control over the Carbon Boundary SBR has been realized which in turn permits stable operation of the system at higher SBR and providing a higher H2 yield for per kilogram of biomass due to activation of both homogeneous and heterogeneous reactions.
Although examples for the present disclosure have been described in language specific to structural features and/or methods, it is to be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed and explained as examples of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202241037110 | Jun 2022 | IN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IN2022/050793 | 9/6/2022 | WO |
